Human Reproduction, Vol. 16, No. 4, 790-800,
April 2001
© 2001 European Society of Human Reproduction and Embryology
Prevention of twin pregnancies after IVF/ICSI by single embryo transfer*
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Abstract |
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 Top Abstract IntroductionMultiple pregnancies after...Methods for recognizing embryos...Clinical experience with SET...Implications for future research...Global discussionRecommendationsReferences |
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Twin pregnancies constitute the most serious complication for both mother and children after IVF/ICSI treatment, but transfer of at least two `best looking' embryos remains the standard policy. This is due to our inability and reluctance to identify both the `twin prone' patient and the top quality embryo. Some centres now electively transfer a single embryo (eSET) when particular embryo quality and patient criteria are met. Results from several centres were presented during an ESHRE Campus Course, held on May 6th 2000. Sound clinical trials are needed to clarify several points of discussion. What is the clinical profile of patients in whom eSET should be considered? Will the overall (ongoing) pregnancy rate of the IVF/ICSI programme decrease if eSET is performed in these patients? What is the twinning rate when eSET is a routine policy? Will the financial gain by avoiding perinatal hospitalization costs of prevented twins be balanced by the likely need to perform a number of extra IVF/ICSI cycles? What will be gained by freezing the extra number of high quality embryos? Should eSET be performed at the 2 pronuclear stage, the early cleaving embryo or the blastocyst stage? Common sense dictates that eSET as a concept should be applied from now onwards.
Key words: elective single embryo transfer (eSET)/ICSI/IVF/prevention/twin pregnancies
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Introduction |
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TopAbstractIntroductionMultiple pregnancies after...Methods for recognizing embryos...Clinical experience with SET...Implications for future research...Global discussionRecommendationsReferences |
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The substantial increase in both maternal and neonatal mortality and morbidity in twin pregnancies is well-documented (Bergh et al., 2000
). An ESHRE Capri Workshop held in August 1999 (ESHRE Capri Workshop Group, 2000) studied these risks in depth and stressed the urgent need for prevention. The incidence of multiple gestation in most countries has almost doubled since the introduction of assisted reproductive technology (ART), which has now become the major source of all high order multiple pregnancies. The possibility of transferring only one embryo as the ideal and logical means for prevention of twins was not mentioned in the Capri report. The present ESHRE Course was organized to explore the possibility of using elective single embryo transfer (eSET) as a method of reducing the incidence of twins in twin-prone IVF/ICSI-patients. The average number of oocytes collected nowadays varies between 10 and 15, a large excess considering that only one to three embryos will be transferred. This strategy is perpetuated because there is a strong belief that outcome of treatment is correlated with the number of oocytes retrieved which allows choice of the best embryos. To increase their success rate, most IVF centres have indulged in the transfer of multiple embryos, resulting in more than half of the children born after IVF originating from multiple gestation pregnancies. This fact has been accepted in the past, if not as a boon to the patient at least as an unavoidable consequence.
High order multiple pregnancies are no longer accepted as an unavoidable side-effect of IVF. In many, although regrettably not all, IVF centres, the replacement of two embryos is now considered as a standard policy. Although this is a recommendable step forwards, this policy will have little effect on the incidence of twin pregnancies. The incidence of twin pregnancies in IVF programmes which have adopted this policy varies between 20 and 35%. It is suggested that infertility specialists should strive to reduce the incidence of twin pregnancies. In fact, in contrast with ovarian stimulation, the outcome with regard to the number of gestations is largely in the hands of the doctor and the patient.
A number of reasons why the problem of multiple pregnancy, including twin pregnancy, is not yet solved are summarized in the following ten points: (i) Lack of efficiency of IVF, necessitating the transfer of more than one embryo. (ii) Poor predictability of embryo survival and implantation potential. (iii) Overall poor results of cryopreservation programmes. (iv) Insufficient information to the couple on the risks of multiple gestation. (v) Emotional and financial burden of ART treatment, pushing patients and doctors alike to improve the results at the expense of an increased risk of multiple gestation. (vi) Infertility specialists are frequently not involved in obstetric care and hence have no direct feedback from the obstetric outcome of their treatment successes. (vii) Success of IVF is too often expressed as pregnancies instead of healthy born children per cycle. (viii) Lack of enforcement by journal editors to express results in terms of singleton pregnancies and healthy children. (ix) Lack of strong and formal guidelines concerning embryo transfer and ovarian hyperstimulation. (x) Lack of a regulatory body.
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Multiple pregnancies after IVF/ICSI: clinical aspects of current practice |
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TopAbstractIntroductionMultiple pregnancies after...Methods for recognizing embryos...Clinical experience with SET...Implications for future research...Global discussionRecommendationsReferences |
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The biology of monozygotic and dizygotic twinning, the long-term outcome and the relative inability of modern obstetrical care to significantly improve neonatal outcome in twins, were studied during a recent ESHRE Capri Workshop (ESHRE Capri Workshop Group, 2000
). These well-known facts and data were briefly repeated during the present workshop but will not be recapitulated here. Two additional perspectives were added, as follows.
A comparison between both singleton and twin pregnancies from spontaneous and IVF pregnancies indicates an inferior outcome for IVF pregnancies
In IVF pregnancies increased rates of pregnancy complications as well as impaired neonatal outcomes have been reported. This has often been ascribed to the increased incidence of multiple pregnancies after IVF. However, in 1985 the Australian In Vitro Fertilization Collaborative Group was the first to mention a high incidence of preterm birth and low birth weight in singleton IVF pregnancies (Australian IVF Collaborative Group, 1988). Since then, a number of studies on IVF singleton and twin pregnancies have been published with conflicting results. A major problem in the judging of the outcome of IVF pregnancies is the choice of a control group. Comparison to national data derived from the general patient population is hampered by differences between the IVF group and the general population, i.e. IVF mothers are usually older and of lower parity than their counterparts who conceived naturally. This problem was tackled in two ways. First, a study was conducted in singleton and in twin pregnancies in which IVF pregnancies were compared to a group of control pregnancies after matching for variables such as age, parity and medical and obstetrical history. Second, a study was performed in singleton pregnancies in which IVF pregnancies were compared with a group of spontaneous pregnancies, and correction for confounding factors was performed by regression analysis. Four Dutch University Centres participated in this study (Koudstaal, 1999).
The course of pregnancy and perinatal outcome of ongoing singleton IVF pregnancies were compared to those of spontaneous singleton pregnancies after matching for maternal age, parity, ethnic origin, height, weight, smoking habit, obstetrical and medical history, date of delivery as well as the hospital that provided the obstetrical care. A total of 307 IVF and 307 control pregnancies were entered into the study. The main results were a shortened gestational length of 272 versus 277 days (P = 0.005) (in pregnancies with spontaneous onset of labour 272 versus 275 days, P = 0.05), an increased prematurity rate (15 versus 5.9%, P < 0.001) and an increased small for gestational age rate (16.2 versus 7.9%, P < 0.001) in IVF pregnancies. Placental weight in both groups was comparable (534 ± 148 g versus 531 ± 132 g, P = 0.74). Consequently, the placenta/birth weight ratio was higher in the IVF group (0.18 ± 0.05 versus 0.17 ± 0.06, P = 0.01). IVF children needed longer neonatal care (3.6 ± 0.92 days, versus 2.3 ± 0.73 days, P = 0.04) as well as longer neonatal intensive care (0.4 ± 0.31 days, versus 0.02 ± 0.7 days, P = 0.03). In a second study 1465 singleton IVF pregnancies were compared to 2061 singleton pregnancies after natural conception. In both groups only pregnancies in which the infant was born alive were included. The IVF pregnancies originated from 25 (of the 41) IVF Dutch IVF clinics. The control pregnancies group was derived from the Social Medical Survey of Children attending the Child Health Clinics. IVF mothers were older (33.7 versus 28.9 years, P < 0.001), more often primiparous (68.6 versus 42.6%, P < 0.001) and more highly educated. The pregnancy outcome showed substantial differences. In the IVF group gestational age at birth was shorter (275.6 versus 278.4 days, P < 0.001) and preterm birth occurred more often (9.3 versus 5.2%, P < 0.001). Mean birth weight in the IVF group was less than in controls (3247 g versus 3433 g, P < 0.001) and the rate was higher (13.8 versus 9.7%, P < 0.001). The difference in mean birth weight of 186 g to the detriment of the IVF group might be explained by the differences in maternal characteristics as well as the lesser gestational age at birth in IVF pregnancies. However, after adjustment by linear regression analysis for maternal, demographic and lifestyle factors, infant sex and gestational age, the difference was still 90 g. The adjusted difference in gestational length was 2.3 days, the adjusted odds ratio for preterm birth 1.4 (95% CI = 1.2–1.7). In conclusion: it was found that in comparison to their naturally conceived peers IVF singletons were born earlier and with lower birth weight, even when adjusted for gestational age.
In the same hospitals and in a similar manner as described above, IVF twin pregnancies were compared to carefully matched controls (Kondstaal, 1999). In 96 IVF twin pregnancies mean gestational age at birth was 6 days less than in controls, however, this difference was not significant. In cases with spontaneous onset of labour the difference was 9 days but again, statistically insignificant. Mean birth weight of both children was less in the IVF group than in controls (228 g versus 2407 g, P = 0.04), no difference was found in the rate in both groups. In judging these results it should be noted that the design of this study precluded matching by zygosity. This implies that the composition of the IVF group was basically more favourable than the control group as the rate of monozygous twins in the latter will be substantially higher (according to our calculation 39% in the control group and 10% in the IVF group). Monozygous twins are known to have an impaired pregnancy outcome in comparison to dizygous twins, so pregnancy outcome of the IVF group should be better than that of the controls. However, a slightly poorer pregnancy outcome was observed in the IVF group.
From these studies it can be concluded that pregnancy outcome of singleton and twin pregnancies is impaired in comparison to naturally conceived pregnancies. The cause (or combination of causes) is unknown. Potential causes are the infertility as such, maternal factors like stress in the pregnancy, the ovarian stimulation that usually accompanies the IVF procedure and the IVF procedure itself.
Transfer of two embryos did not result in any decrease in the incidence of twin pregnancy
As a consequence of work by a number of authors (Staessen et al., 1992, 1993, 1995) showing that triplets can be largely avoided by replacing no more than two embryos without decreasing significantly the overall pregnancy rate, replacing the two best looking embryos has been the recommended standard of care in IVF/ICSI practice for ~10 years now. This work has been confirmed by later studies (Templeton and Morris, 1998). In most countries, a stagnation or a slight decrease in the number of triplets has been observed since this standard has been applied, indicating that both physicians and patients still yield too quickly to the expectant pressure of patients to transfer three embryos. The incidence of twins, however, has not decreased and lingers around 25%. Therefore, the least one can conclude is that either we have to live with a tremendous iatrogenic pathology, easily underestimated both by patients and doctors, or we have to rethink fundamentally our transfer policy, considering single embryo transfer. It is clear that in doing this, there is a very strong impetus to develop methods for recognizing embryos with a very high implantation potential. However, finding and comparing such methods must not detract us from the real goal which is not how to obtain pregnancy rates as high as possible at an `acceptable' complication rate, but which is how to obtain complication rates as low as possible at an `acceptable' pregnancy rate, e.g. a rate similar to that of normally fertile couples.
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Methods for recognizing embryos with high implantation potential after IVF/ICSI |
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TopAbstractIntroductionMultiple pregnancies after...Methods for recognizing embryos...Clinical experience with SET...Implications for future research...Global discussionRecommendationsReferences |
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Criteria have to be formulated that allow the identification of embryos with very high implantation potential. The question is whether such an embryo can be identified as early as the zygote stage, or whether further development to the early cleavage stages or to the blastocyst stage is necessary or can improve the selection. Clinical trials will have to be conducted to clarify these technical aspects, whereas the fundamental option to transfer only one embryo when certain conditions are met, could be considered from now onwards. These conditions are not so rare as those who hesitate to apply eSET seem to think, since some ongoing programmes now transfer one single embryo in up to 25–30% of all their transfers without a significant drop in their overall pregnancy rate (Gerris et al., 2000
; de Sutter et al., 2000). An approach destined to be applied worldwide by as many IVF programmes as possible, should be easy to apply, easy to learn, reproducible and cheap. It must also be considered a possibility that methods to identify high implantation embryos at any stage could be used in a complementary fashion. There should also be made a clear distinction between concepts and findings that shed new light on early human embryonic development as a biological phenomenon per se and practical clinical approaches that are easily applicable in daily practice.
Perifollicular vascularity and outcome in clinical IVF
Quantifiable characteristics of perifollicular vascularity, determined noninvasively by colour pulsed Doppler ultrasonography, appear to be associated with the developmental competence of the corresponding oocyte. Measurements of blood flow characteristics associated with specific, fully-grown preovulatory follicles produced in stimulated cycles indicate levels of perifollicular vascular expansion that correlate with the normality of embryo development during in-vitro culture and with increased frequencies of implantation and normal term gestation after uterine transfer. Biochemical evidence exists which suggests that differences in vascular development and blood flow between follicles are related to the ability of each follicle to sense and respond to hypoxia by up-regulating the expression of hypoxia-inducible transcription factors, which in turn may co-ordinate the expression of potent angiogenic growth factors. If confirmed by additional clinical experience, the ability to identify specific perifollicular vascular phenotypes by ultrasonography associated with normal developmental competence for the oocyte and embryo, combined with an understanding of the underlying molecular biology that may be involved in their generation, could be important prognostic indicators of developmental potential and clinically relevant in the selection of embryos for transfer (Van Blerkom et al., 1997; Van Blerkom, 1998). These findings may also explain the different outcomes from assisted-conception treatments observed in women of advanced reproductive age and patients with different infertility histories. Current findings from several IVF programmes suggest that for a typical stimulated cycle, less than 40% of fully-grown follicles show perifollicular blood flow indices associated with competent oocytes. However, implantation rates in excess of 50–60% have been reported when two or three cleavage stage embryos that developed from such oocytes are transferred on day 2 or 3. These results suggest that efforts directed at assessing perifollicular vascularity could have an important role in limiting the number of embryos transferred while not adversely compromising outcome.
Do nuclear and cytoplasmic polarities in human pronuclear eggs provide clinically relevant insights into developmental competence?
The pronuclear stage of human embryogenesis is associated with progressive changes in cytoplasmic organization, pronuclear orientation, and nucleolar alignment. These changes have been suggested to provide visible indications of developmental competence and when replaced in IVF cycles, cleavage stage embryos that displayed these characteristics at the 1-cell stage have been reported to have high implantation potential. Temporal and spatial aspects of polarities in pronuclear stage human eggs can be described that provide relevant cell biological information as to how they may be generated, and why they may or may not be indicative of developmental competence (Antczak and Van Blerkom, 1999). Current evidence suggests that for a typical cohort of fertilized eggs produced in stimulated IVF cycles, polarized characteristics occur in only some pronuclear eggs. Limiting transfers to one or two cleavage stage embryos that showed appropriate polarized characteristics at the 1-cell stage may increase the probability of pregnancy without the attendant risk of higher order gestations. In addition, the presence or absence of polarized phenotypes with respect to recent findings indicates that first polar body morphology and relative size of the perivitelline space in the MII oocytes may indicate developmental potential after fertilization. A final aspect of polarization to be described comes from recent studies (Van Blerkom et al., 2000) concerning differential mitochondrial distributions in pronuclear human eggs. Evidence exists that shows how different patterns of mitochondrial distribution result in quantitative differences in mitochondrial inheritance between blastomeres, and why certain patterns of inheritance correlate negatively with developmental competence (Van Blerkom et al., 1998, 2000). These genetically determined phenomena may give a relatively simple explanation to the apparently complex phenomenon of extreme differences in embryo morphology and implantation potential (Van Blerkom et al., 1998, 2000). They certainly allow us to question once more the rationale for culturing embryos until the blastocyst stage.
Selection of a top quality day 3 embryo for IVF/ICSI: a necessary step prior to single embryo transfer
In order to identify which embryos have the highest implantation potential, the morphologic characteristics of embryos with proven 100% implantation were first determined in a retrospective study, as a step prior to elective single embryo transfer. Subsequently, an attempt was made to refine these criteria by proposing a way of calculating the individual implantation potential of embryos, which can be used when performing elective single embryo transfer.
Characterization of a top quality embryo, a step towards single embryo transfer
The common characteristics were determined of 46 embryos with proven ongoing implantation. These embryos originated in 23 cycles and led to 23 double embryo transfers resulting in 23 ongoing twin pregnancies. These characteristics were: absence of multinucleated blastomeres, a maximum of 20% fragmentation on day 3 and a cleavage rate of four or five blastomeres on day 2 and at least seven on day 3.
Estimation of the individual implantation potential of embryos
An attempt was made in women <38 years of age to establish a parameter describing the relative implanting behaviour of each type of embryo. Therefore, only embryos transferred on day 3 and with documented implantation behaviour were considered. Of 1540 embryos in 745 transfers, 213 with proven implantation behaviour could be selected. These originated from 40 eSETs resulting in 40 ongoing pregnancies, one eSET leading to one ongoing monozygotic twin pregnancy, 78 elective double embryo transfers (eDET) leading to 78 ongoing twin pregnancies, two eDETs leading to two ongoing dizygotic twin pregnancies and four triple embryo transfers leading to four ongoing triplets. Of these 213 embryos with 100% ongoing implantation 151 (71%) showed 10% or less fragmentation, 55 (26%) showed between 10 and 20% fragmentation, while only seven (3%) showed more than 20% fragmentation. In only one of these 213 embryos was multinucleation observed and this embryo was also more than 20% fragmented. Because embryos with more than 20% fragmentation as well as embryos with multinucleation form only a minor part (3%) of the implanting embryos they were not investigated in further detail.
Apart from this group of embryos with 100% proven implantation there is another group where there is absolute certainty regarding their implantation behaviour, namely those embryos without any implantation, i.e. those followed by a negative HCG after transfer. By calculating for each type of embryo (with identical fragmentation and cleavage pattern) the ratio between the number with 100% implantation and the number with known implantation (i.e. the sum of those with 100% implantation and those with 0% implantation), the implanting fraction is obtained. This parameter offers a relative comparative measure for the implantation potential and allows a qualitative ranking of different types of embryos. The embryos with known implantation represent 65% of all transfers and 54% of all implanted embryos.
Extrapolation to embryos with unknown implantation behaviour
An equation can be established linking the total number of implantations and the sum of the implanted numbers for each type of embryo. From this equation a correction factor of 1.095, essentially reflecting the endometrial factor and the effect of the transfer technique, could be calculated. Multiplying the observed implanted fractions with this correction factor and with 100, results in a figure reflecting the individual implantation potential for each embryo, expressed as a percentage, the highest value being 47 for the embryos with the ideal cleavage pattern of 4-cells on day 2 and 8-cells on day 3, i.e. similar to the highest figures shown for selected groups of embryos reaching the blastocyst stage. This suggests that the high implantation potential embryo has this capacity throughout its development probably right from the beginning.
Prolonged embryo culture to the blastocyst stage as a means of avoiding twin pregnancy: a critical appraisal
Following fertilization either by IVF or ICSI, the in-vitro human embryo undergoes several cleavage divisions, compacts and cavitates to form a blastocyst over a period of 4 to 5 days. During this time, the energy substrate requirements change from a dependence mainly on simple tricarboxylic cycle intermediates such as pyruvate in early cleavage to glucose at the blastocyst stage. This change in the ability to utilize different substrates probably mirrors changes in the oviduct and uterus in vivo as the embryo progresses down the female reproductive tract prior to implantation. Until recently the media used for human embryo culture were largely based on those developed for animal, often mouse, embryos or tissue culture with high concentrations of both energy substrates. In these media, many embryos arrest at cleavage and morula stages and only about half reach the blastocyst stage. Furthermore, some blastocysts are clearly abnormal, only a small proportion hatch from the zona pellucida in vitro and clinical pregnancy rates following transfer of morulae or blastocysts were reported to be low or certainly no better than at cleavage stages.
Recently, sequential media have been developed to reflect the changing needs of the embryo at different stages of preimplantation development (Gardner, 1998; Gardner and Lane, 1998). Improved rates of development to the blastocyst stage have been reported and clinical pregnancy and implantation rates following multiple blastocyst transfers are significantly higher than at cleavage stages (Gardner et al., 1998a,b; Gardner and Schoolcraft, 1999). This has led to the suggestion, but, as yet, not to the clinical proof, that the use of these media combined with prolonged culture to the blastocyst stage may allow single embryos to be transferred thus minimising the risk of multiple pregnancies (Marek et al., 1999; Gardner et al., 2000).
There is no doubt that the study of the human blastocyst has been extremely useful in elucidating a number of molecular mechanisms of early cleavage, differentiation and genetic control of early development. The blastocyst is a very interesting pre-implantation stage of the human being that holds a number of theoretical advantages over earlier stages with respect to our understanding of in-vivo mechanisms. Moreover, it is the stage at which in-vivo implantation occurs. However, to date no published data on the elective transfer of one blastocyst are available although this is obviously only a matter of time. From published data on transfer of two blastocysts (mostly retrospective) the possibility cannot be ruled out that with elective single blastocyst transfer, implantation (and hence, pregnancy) rates could be obtained that are similar or even superior to those reported for single cleaving embryos. However, two methodological caveats must be formulated. First, it will not suffice to compare highly selected blastocysts with `the best looking day three embryo'. On the contrary, blastocysts have to be compared with strictly selected day 3 embryos, i.e. using validated strict criteria. Second, any comparison should be made on the basis of ongoing pregnancies per started cycle, i.e. what the patient is interested in, without the use of intermediate inclusion criteria such as the presence of at least 10 follicles at the time of human chorionic gonadotrophin (HCG) administration or the presence of at least 10 oocytes or at least four good quality embryos at day 3 after fertilization, etc. which constitute a selection bias. In addition, when data on single blastocyst transfer appear, it will be time to ask at what price these results have been obtained, not only financially, but also psychologically (for instance in the proportion of drop-outs).
The only methodologically correct prospectively controlled randomized trial published to date comparing day 5 versus day 3 transfer of two embryos did not find a significant difference in pregnancy rate between both groups (Coskun et al., 2000). Moreover, the limitations attributed to some of the reports on day 3 eSET (women >34 years in their first IVF/ICSI cycle) were dictated by ethical considerations pertaining to a clinical study. When data were analysed irrespective of age up to 38 years and of the rank of the trial, results remained unchanged.
In addition, there is no correlation between the morphological aspect of blastocysts and their genetic constitution. The initial idea that culture to the blastocyst stage automatically selects the genetically normal embryos does not hold (Evsikov and Verlinsky, 1998).
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Clinical experience with SET as a prevention of twins after IVF/ICSI |
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TopAbstractIntroductionMultiple pregnancies after...Methods for recognizing embryos...Clinical experience with SET...Implications for future research...Global discussionRecommendationsReferences |
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Several speakers reported their experience with single embryo transfer. At present, no data are available on systematic single embryo transfer in selected patients using day 1 (zygote stage) (Scott and Smith, 1998
) or day 5 (blastocyst) stage embryos. A summary of published results, and those presented at the ESHRE Workshop, is given in Table I.
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The Scandinavian experience
In Finland, the number of multiple pregnancies has increased with the increasing pregnancy rate (PR) after IVF and ICSI. In 1993 the policy of transferring only two embryos was accepted in Finland. However, the number of twin pregnancies is still high (Table II
). Based on the high number of twin pregnancies the health care costs for one IVF newborn have been estimated to be 5.4 fold compared with other newborns (Gissler et al., 1995). The psychological and social consequences of a multiple pregnancy should be considered (Doyle, 1996). Couples are requesting a singleton pregnancy more and more frequently. Therefore, in Finland the number of elective single embryo transfers has shown an increasing tendency since 1997, reaching 19.7% of all cycles during 1999. Vilska et al. first recommended single embryo transfer for medical indications such as diabetes or other chronic disease of the woman, previous hysterotomy, uterine malformation, risk for severe ovarian hyperstimulation syndrome or indication for prenatal diagnosis. This policy of embryo transfer resulted in a PR of 29.7% per embryo transfer, which is considered to be acceptable and encouraging. The cumulative PR in these subjects was 47.9% per oocyte retrieval at a time point when some subjects still had frozen embryos in storage (Vilska et al., 1999). Individualizing the embryo transfer policy is the only way to minimize the risk of a multiple pregnancy without compromising the PR. Both the clinical and embryological factors are important in helping us to recognize the couples at risk for a twin pregnancy (Gerris et al., 1999) and to optimize the indications for eSET. Further data from the same group indicate that when the extra pregnancies obtained after freezing/thawing of embryos remaining after eSET in the fresh cycle are added, a cumulative pregnancy per oocyte retrieval was obtained of 48% (Tiitinen et al., 2000) (Table III).
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Another group from Finland (J.Tapanainen et al., unpublished data) showed their experience with eSET (Table I
). A total of 143 women, who had at least four good quality embryos available after IVF/ICSI and had a maximum of two previous failed treatment cycles, were randomized to have either one or two embryos transferred. The study groups did not differ as regards age, aetiology of infertility or ovarian response and the ART method used. The clinical pregnancy rate per transfer was 31.0% in the one embryo transfer group and 44.3% in the two embryo group (not significant). The implantation rate per embryo was similar in both groups (31 versus 30%). Two embryo transfer resulted in nine twin deliveries (36%), and there was one monozygotic twin delivery in the one embryo transfer group. The cumulative clinical pregnancy rate after fresh and cryopreserved embryo transfers was 46% in the one embryo transfer group and 53% in the two embryo transfer group. The number of preterm deliveries (<37 weeks) was 20% in the two embryo group and 5% in the one embryo group, and the number of low birthweight babies (<2500 g) was nine and two, respectively. In this group, results were also augmented by adding pregnancies obtained after cryopreservation and thawing of embryos. These results indicate that a very acceptable pregnancy rate was achieved by transferring only one embryo in a selected patient population. On the basis of the success rates in this study and in our overall patient population we have estimated that maximally five more pregnancies would be obtained in the two embryo transfer group as a result of fresh and cryopreserved embryo transfers. When the treatment methods are evaluated the costs associated with maternity and neonatal health care should also be taken into account. Our results support the assumption that one embryo would be more cost-effective than two embryo transfer.
The situation in Sweden was summarized by Hägglund (Table I). In Sweden, as in the other Nordic countries, all pregnancies and deliveries are routinely registered at the National Health Register. Units providing IVF have an obligation to report annually to the National Health Register all treatments of assisted reproductive technology. A comparison between these two registers made it possible to evaluate the outcome of all babies born after IVF (n = 5856) and babies born in the general population (n = 1 505 724) between 1982 and 1995 (Bergh et al., 2000). The continuing evaluation has added another 3255 babies born during the period 1996 to 1997.
The Swedish registry study stated that almost all pregnancy and neonatal complications in IVF pregnancies were due to multiple pregnancies (Bergh et al., 2000).
During the period 1982–1997 a successful lowering of the number of transferred embryos from four or more to a routine of two embryos transferred, was performed without jeopardizing the overall pregnancy rate (Swedish register 1997: 33% clinical pregnancies per transfer).
Based on previous experience of reduction of the number of embryos transferred and the preliminary results coming out of Finnish data, single embryo transfer is the most seriously considered option in Sweden today.
Until now, experiences with single embryo transfer could only be gained from non-elective single embryo transfers. The National Health Register showed figures varying between 6 and 12.1% clinical pregnancies per transfer between 1994–1997 (P.-O.Karlström, personal communication). Single units like Sahlgrenska University Hospital have reported an average of 17.6% (41/232) clinical pregnancies per non-elective single embryo transfer between 1995 and 1999 (C.Bergh, personal communication).
At the International Fertility Center in Malmö, Sweden, 26 elective single embryo transfers were performed in 1998 and 1999. These resulted in seven single deliveries (baby take home rate 27%) (Table I). There were no multiple pregnancies.
In Sweden, two separate prospective, randomized multicentre trials will be launched during the year 2000.
The first trial will be coordinated by the Sahlgrenska University, Gothenburg. It has a cross-over design and intends to evaluate the pregnancy rate in a group at high risk of conceiving with a multiple pregnancy (<35 years of age), with regard to their individual characteristics (tubal/non-tubal; number of good quality embryos), as outlined elsewhere (Hazekamp et al., 2000). The second trial will be performed by the University of Lund and will include 350 couples were the female is <39 years of age. The primary aim is to evaluate the pregnancy rate if one or two embryos are replaced, respectively, in, if necessary, two consecutive cycles. A secondary aim is to estimate the differences in total costs of the pregnancies (hospitalization, loss of income, neonatal and postnatal costs).
The Flemish experience
Data from Ghent
When considering how to reduce the multiple pregnancy rate in IVF, most authors stress the need for further research into laboratory aspects reflecting embryo quality, such as prolonged in-vitro culture, embryo coculture techniques, or embryo biopsy with preimplantation genetic analysis (Bronson et al., 1997; Meldrum, 1999; Schoolcraft et al., 1999). This is rather a fatalistic view that ignores the possibility of further reducing the number of embryos per transfer, even with our current limited insight into the process of embryo implantation.
We need to consider an individualized embryo transfer policy comprising elective transfer of one single embryo in patients at risk for multiple gestation and a more liberal attitude for those with a less good prognosis. In fact, this is just an extrapolation of current prognostic models used to determine the optimal number of embryos to be transferred (Steer et al., 1992; Roseboom et al., 1995; Hu et al., 1998; Martin and Welch, 1998; Wheeler et al., 1998). Would this reduce significantly the number of multiple pregnancies without dramatic fall in overall success rates? We tried to anticipate the effect of such a strategy on our IVF results, in terms of the overall pregnancy rate and multiple pregnancy rate (Coetsier and Dhont, 1998).
eSET has been progressively introduced into the programme in Ghent since 1997. A matched case-control study was performed. All patients undergoing a single or a double embryo transfer in our centre since 1997 were selected for this study. There were 126 patients who underwent an elective SET (having more than one embryo available for transfer) (group 1) and 100 who underwent a non-elective SET (only one embryo available) (group 2). Similarly we selected 1293 patients with an elective double embryo transfer (DET) (group 3) and 136 with a non-elective DET (only two embryos available) (group 4). Data concerning pregnancy outcome were compared between these groups, using 
2 statistics.
Patients in groups 2 and 4 were significantly older than in groups 1 and 3. There was no difference between the age of women in groups 1 and 3 on one hand and groups 2 and 4 on the other. To compare transfers with the same embryo quality, group 1 was split into a group who received an excellent embryo and a group who received a good embryo, and group 3 into three subgroups (two excellent, one excellent and one good, and two good embryos transferred). Transfers of moderate embryos were excluded. Results are shown in Table IV.
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Our data confirm that non-elective single or double embryo transfer yields poor results compared to elective SET or DET. These results further confirm that elective single embryo transfer is a valid option to reduce the incidence of multiple pregnancies after ART. Moreover, the fact that pregnancy rates between groups 1 and 3 do not differ, even after correction for the quality of the transferred embryos, indicates that the implantation rate per embryo is higher in the eSET group than in the eDET group.
Data from Antwerp
The Antwerp experience with single embryo transfer as prevention of twin pregnancy after IVF/ICSI is based on a combination of efforts at determining morphological criteria on day 2 and day 3 of embryo culture of high implantation embryos and subsequent clinical application of these criteria.
• Identification of a top quality embryo
In current practice, the two `best looking' embryos are used for transfer. However, we wanted to identify by means of strict criteria embryos with a high implantation potential on day 3. We therefore analysed the morphological and growth characteristics of 46 embryos all leading to ongoing twin pregnancies. This led to our description of a top quality day 3 embryo (Van Royen et al., 1999): top quality embryos were defined as exhibiting all of the following characteristics: four or five blastomeres on day 2 and at least seven blastomeres on day 3 after fertilization, absence of multinucleated blastomeres and <20% of fragments on day 2 and day 3 after fertilization. These characteristics have been fine-tuned recently so as to allow us to predict the implantation potential of each individual embryo based on growth and morphological characteristics (Van Royen et al., 2001). There is of course some correlation between traditional and strict criteria, but traditional criteria do not always take into account the fact that embryos with multinucleated blastomeres seldom lead to an ongoing pregnancy and with the strict time intervals between subsequent embryo evaluations that are necessary to establish whether a particular embryo is ahead of or behind the optimal cleaving rate. These findings are in harmony with more fundamental observations by van Blerkom (van Blerkom, 1998; van Blerkom et al., 2000) regarding mitochodrial distribution and other characteristics of the early zygote.
• Overall experience with single embryo transfer
It is not advisable to transfer only one embryo to all patients participating in an IVF/ICSI programme. Older patients, patients who have had several unsuccessful treatment cycles, patients who smoke, patients who show predominantly poor quality embryos (Magli et al., 1998) and perhaps other groups of patients are known to have a decreased implantation rate. We validated the strict embryo criteria by reviewing retrospectively a continuous series of 400 IVF/ICSI cycles immediately prior to the start of the prospective study in which we used our criteria but still used the standard approach to embryo transfer (Van Royen et al., 1999).
These data allowed us to consider our embryo selection criteria sufficiently reliable to conduct a prospectively randomized study (Gerris et al., 1999) of which the results are shown partially in Table I. Table V shows the details of this study: eSET (groups A + D1) had an ongoing implantation and pregnancy rate of ~40%, which means that eSET is feasible in twin prone patients and that the ongoing pregnancy rate (OPR) in the SET group is comparable to that of the rest of the IVF/ICSI population receiving two embryos with the exception of those patients receiving two top quality embryos, who have an ongoing pregnancy rate of ~65%.
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Reported experience with SET pertained to a continuous series of 779 IVF/ICSI cycles. Of these, there were 111 single embryo transfers of one top quality embryo (95 elective and 16 compulsory). The ongoing pregnancy rate in this group was similar to that for all the other patients (n = 624) who received a mean of 2.12 embryos. These data indicate that in well-selected patients (in whom ~80% of all twins occur) dizygotic twins can be totally prevented (Gerris et al., 2000
). Table VI shows that similar results were obtained in patients receiving eSET as in those receiving two or more embryos. The small (n = 16, data not shown separately) subgroup with a compulsory SET of one top quality embryo showed clearly inferior results, indicating the importance of the size of the oocyte and/or embryo cohort.
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It has been stated that eSET can only be applied to a very small part of the whole IVF/ICSI population. One of the reasons for this was that in our original study, eSET was proposed only to first trials in women <34 years of age. However, this was only for purely ethical considerations. It took a lot of clinical courage to launch the study altogether. We have tried to assess the size of our IVF/ICSI population which could potentially benefit from the single embryo transfer strategy as a prevention of twin pregnancy: 371/512 (72.5%) of all embryo transfers concerned at least one top quality embryo, in which the principle of twin prevention by performing single embryo transfer of one top quality embryo is applicable. A further analysis of our data, including all women
38 years, shows that all conclusions remain valid, including the age group 34 to <38 years of age. We believe that patients <38 years of age achieving at least one top quality embryo should be offered single embryo transfer for at least one treatment cycle. • The health-economic evaluation
The previous data illustrate that SET is feasible in a significant fraction of the IVF/ICSI patients (in those considered `twin-prone', i.e. at least 25–30% of all cycles) without a significant drop in overall pregnancy rate. The benefits of applying eSET reside not only in the prevention of human suffering, both of neonates and parents, but also in reducing the elevated costs induced by the complications of twin pregnancy (Wolner-Hanssen and Rydstroem, 1998). Before insurers, either public or private, can be induced to create financial incentives, e.g. by refunding (part of) the costs involved in IVF/ICSI laboratory performances, it will be mandatory to prove to them that they as well are likely to gain from it. Therefore, several studies appear now to be ongoing, e.g. in Belgium and in Sweden, that focus on the cost/efficacy balance. Results from these studies will probably become available from the year 2002 onwards.
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Implications for future research and routine clinical practice |
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TopAbstractIntroductionMultiple pregnancies after...Methods for recognizing embryos...Clinical experience with SET...Implications for future research...Global discussionRecommendationsReferences |
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Increasing the number of transferred embryos in patients with less good prognosis is accepted by most infertility centres as a routine procedure and several studies have been published on this subject (Azem et al., 1995
; Adonakis et al., 1997; Hu et al., 1998). This is not the case for the reduction to one single embryo per transfer in patients with good prognosis, although the rationale behind this policy is exactly the same.
Two independent groups consider that single embryo transfer is worth consideration in patients with a good prognosis (Gerris and Van Royen, 2000; Hazekamp et al., 2000). Even with the imperfect embryo selection criteria used currently, such a strategy would probably reduce the overall incidence of multiple pregnancy by half without a dramatic fall in the overall success rate. Although most infertile couples are willing to accept the risk of a twin pregnancy, IVF centres should not ignore the perinatal risks and the familial impact of a multiple pregnancy. The long term welfare of the family should take precedence over the short term goal of achieving a pregnancy and ambiguous preoccupation with success figures. Indeed, a healthy child is the ultimate goal of IVF-treatment, and not `achievement of pregnancy, even multiple', as sometimes stated (Azem et al., 1996).
Over the past few years, the mean number of embryos per transfer has been gradually reduced from four to two (Nijs et al., 1993; Staessen et al., 1993, 1995; Vauthier-Brouzes et al., 1994; Roest et al., 1997; Templeton and Morris, 1998). A further reduction to one single embryo per transfer in good prognosis cases can be acceptable to patients, provided objective information is given on the increased obstetrical and neonatal risk and the added socio-familial burden of twin pregnancies. From the socio-economic point of view, we can state that standard eSET in every IVF patient, even without a favourable prognosis, still is more cost-effective than the replacement of two embryos (Wolner-Hansen and Rydstroem, 1998). We realize that it is not only the patients, but also the IVF centres who have to be convinced to look further than the day of a positive pregnancy test.
The medical profession at large and societies for reproductive medicine in particular could help to promote this policy by stressing that the professional competence of an IVF centre should be measured in terms of ongoing singleton pregnancies per cycle.
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Global discussion |
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TopAbstractIntroductionMultiple pregnancies after...Methods for recognizing embryos...Clinical experience with SET...Implications for future research...Global discussionRecommendationsReferences |
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The solution of the twin problem is simple and for the layman self-evident: transfer of a single embryo. The only way to reduce twin pregnancies indeed is to make single embryo transfer the standard of good medical practice and to look at how we can implement this policy and make it acceptable to patients and infertility specialists. For this policy to be accepted and to give it a chance to be implemented several conditions will have to be fulfilled: proof of its feasibility; determination of the threshold levels of cost benefit in terms of pregnancy rates versus reduction of twin pregnancies; improvement of culture media; selection of oocytes and embryos; selection of patients; making IVF procedures less stressful; improving results of cryopreservation; making IVF more accessible by an agreement on reimbursement; increase the awareness of the perinatal risks of twin pregnancies by both doctors and patients; genetic screening of the preimplantation embryo.
Several groups have now demonstrated that single embryo transfer can be associated with the same pregnancy rates as in the overall IVF population, provided a careful selection of patients and embryos is made. Large scale studies will be needed, however, to validate these criteria and to prove that this policy can have a significant impact on the overall incidence of twin pregnancies.
It is remarkable that the first data on single embryo transfer are derived from day 2 or 3 embryo transfer whereas extended culture of embryos to the blastocyst state is claimed to be associated with higher pregnancy rates per transfer. Randomized prospective studies comparing pregnancy rates following single embryo versus single blastocyst transfer will provide an ideal tool to validate the expectations raised by preliminary studies on blastocyst transfer.
If a reasonable success of eSET can be envisaged, the next question will be whether the current intense stimulation schemes will not become obsolete. It could indeed be argued that the number of oocytes that are produced is far greater than the number of embryos. The experience with the natural cycle, however, with its unacceptably low pregnancy rate, has shown that the oocyte selected by the natural process does not guarantee to produce a viable embryo after IVF. It seems therefore that for the coming years, we will be bound to some kind of stimulation regime. There is indeed a relation between the number of oocytes and the probability of pregnancy. It remains to be demonstrated whether the number of oocytes in itself, by allowing a better selection of embryos, is the important factor or whether the number of oocytes is only a marker of better reproductive capacity of a woman. If this could be established, a point could be made of looking for `softer' stimulation schemes. The availability of GnRH antagonists and recombinant FSH and LH in the near future should allow for more individually adapted stimulation schemes.
This seminar provided the opportunity to exchange data and opinions on a number of issues which have been mentioned and will stimulate ideas and initiatives for fundamental and clinical research with regard to the most important unwanted side effect of IVF/ICSI prevention of twin pregnancies.
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Recommendations |
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TopAbstractIntroductionMultiple pregnancies after...Methods for recognizing embryos...Clinical experience with SET...Implications for future research...Global discussionRecommendationsReferences |
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Although it appears too early to formulate firm and final recommendations for good clinical practice with respect to embryo transfer, a number of statements were made during the Campus Course which can be summarized as follows:
- Twin pregnancy (and, a fortiori, higher order multiple pregnancy) is the most frequent and most severe complication of IVF/ICSI, leading to significant suffering and spiralling obstetrical and neonatal costs.
- A twin (and higher order multiple) pregnancy rate of 25% or more is not acceptable and must induce practitioners to elaborate an individualized embryo transfer strategy, aiming at reducing this incidence to perhaps around 10%.
- An ongoing pregnancy rate of 30% or more per started treatment cycle, i.e. similar to the monthly fecundity in normal fertile people, should be (made) acceptable to all parties involved. Higher rates at the cost of more twins (and higher order multiples) are undesirable.
- Elective SET should be recommended without further delay if at least two conditions are fulfilled:
- The patient is twin prone. This definition needs to be further fine-tuned by further well-designed clinical studies, but currently includes: age (definitely if <34, probably if <38 years of age) and rank of trial (first trial, probably second as well);
- If a `top-quality embryo' can be transferred.
- If a `top-quality embryo' can be transferred.
- The patient is twin prone. This definition needs to be further fine-tuned by further well-designed clinical studies, but currently includes: age (definitely if <34, probably if <38 years of age) and rank of trial (first trial, probably second as well);
- Medical SET should be recommended when a twin pregnancy should be prevented for medical reasons, e.g. cervical incompetence, previous premature delivery, congenital uterine anomalies, indication for prenatal diagnosis and single women, among others.
- How to select an embryo with very high implantation potential remains a matter of debate, but it is secondary to the ethical decision to consider eSET in a responsible programme. Further prospectively randomized clinical studies with randomization prior to stimulation are needed, comparing transfer of one embryo versus one embryo at whatever stage of its development, thereby striving at using a cumulative algorithm that integrates all useful criteria rather than excludes some and swears by others.
- The SET principle should also be kept in mind in cycles where frozen/thawed embryos are used.
- Financial considerations, though understandable in the context of specific health-insurance policies, should in the long run not be used to explain away complications following from multiple pregnancies that are unacceptable if seen from an ethical point of view. The best approach is to show insurers and patients that the limited costs of reimbursement of IVF/ICSI laboratory work will be regained by the prevention of large costs for obstetrical, neonatal and educational costs in children from multiple pregnancies.
It is likely that cultural differences in their broadest sense will continue to play a role in embryo transfer policy. It is important that guidelines originate from our professional group and not from short-sighted and one-sided political thinking. eSET should not be forced upon either doctors or patients, but it should be introduced gradually into daily practice. It is calculated that if 25–30% of all transfers are eSETs, the incidence of twins will gradually come down from the present day 25–30% to an estimated 12–15% of all pregnancies. This is a realistic goal. Countries with some kind of IVF/ICSI-reimbursement will probably take the lead whereas countries where IVF/ICSI is very expensive for the patient will be slower to follow. Elective SET must not be considered in an uncritical and linear way as the standard of care, but rather as the ideal to which we should strive, taking into account the many objective and subjective variables that give our work its human depth.
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Notes |
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To whom correspondence should be addressed: J.Gerris, Center for Reproductive Medicine, Middelheim Hospital, Lindendreef 1, 2020, Antwerp, Belgium. E-mail: jan.gerris{at}ocmw.antwerpen.be
* An ESHRE Campus Course was organized on May 6th 2000 in Antwerp, Belgium with an educational grant from Serono Symposia and the Marguérite-Marie Delacroix Foundation for the prevention of cerebral palsy. The speakers included: T.Coetsier (Ghent), P.Devroey (Brussels), M.Dhont (Ghent), R.G.Edwards (Cambridge), H.Evers (Maastricht), L.Hägglund (Malmö), A.Handyside (Leeds), J.Gerris (Antwerp), J.Koudstaal (Utrecht), S.Vilska (Helsinki), J.Tapanainen (Oulu), J.van Blerkom (Boulder, Colorado), P.van Dop (Eindhoven) and E.Van Royen (Antwerp). 
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References |
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Submitted on September 7, 2000; accepted on January 11, 2001.
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 N. S. Green Risks of Birth Defects and Other Adverse Outcomes Associated With Assisted Reproductive Technology Pediatrics, July 1, 2004; 114(1): 256 - 259. [Full Text] [PDF]
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G. Griesinger, K. Dafopoulos, A. Schultze-Mosgau, R. Felberbaum, and K. Diedrich What is the most relevant standard of success in assisted reproduction?: Is BESST (birth emphasizing a successful singleton at term) truly the best? Hum. Reprod., June 1, 2004; 19(6): 1239 - 1241. [Abstract] [Full Text] [PDF]
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 T. Jain, S. A. Missmer, and M. D. Hornstein Trends in Embryo-Transfer Practice and in Outcomes of the Use of Assisted Reproductive Technology in the United States N. Engl. J. Med., April 15, 2004; 350(16): 1639 - 1645. [Abstract] [Full Text] [PDF]
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J. Gerris, P. De Sutter, D. De Neubourg, E. Van Royen, J. Vander Elst, K. Mangelschots, M. Vercruyssen, P. Kok, M. Elseviers, L. Annemans, et al. A real-life prospective health economic study of elective single embryo transfer versus two-embryo transfer in first IVF/ICSI cycles Hum. Reprod., April 1, 2004; 19(4): 917 - 923. [Abstract] [Full Text] [PDF]
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R. P. Dickey, B. M. Sartor, and R. Pyrzak What is the most relevant standard of success in assisted reproduction?: No single outcome measure is satisfactory when evaluating success in assisted reproduction; both twin births and singleton births should be counted as successes Hum. Reprod., April 1, 2004; 19(4): 783 - 787. [Abstract] [Full Text] [PDF]
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L. A. Schieve and M. A. Reynolds What is the most relevant standard of success in assisted reproduction?: Challenges in measuring and reporting success rates for assisted reproductive technology treatments: What is optimal? Hum. Reprod., April 1, 2004; 19(4): 778 - 782. [Abstract] [Full Text] [PDF]
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J. K. Min, S. A. Breheny, V. MacLachlan, and D. L. Healy What is the most relevant standard of success in assisted reproduction? The singleton, term gestation, live birth rate per cycle initiated: the BESST endpoint for assisted reproduction Hum. Reprod., January 1, 2004; 19(1): 3 - 7. [Abstract] [Full Text] [PDF]
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S. Koivurova, A.-L. Hartikainen, U. Sovio, M. Gissler, E. Hemminki, and M.-R. Jarvelin Growth, psychomotor development and morbidity up to 3 years of age in children born after IVF Hum. Reprod., November 1, 2003; 18(11): 2328 - 2336. [Abstract] [Full Text] [PDF]
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R. D. Lambert Safety issues in assisted reproductive technology: Aetiology of health problems in singleton ART babies Hum. Reprod., October 1, 2003; 18(10): 1987 - 1991. [Abstract] [Full Text] [PDF]
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V. Soderstrom-Anttila, S. Vilska, S. Makinen, T. Foudila, and A.-M. Suikkari Elective single embryo transfer yields good delivery rates in oocyte donation Hum. Reprod., September 1, 2003; 18(9): 1858 - 1863. [Abstract] [Full Text] [PDF]
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A. Tiitinen, L. Unkila-Kallio, M. Halttunen, and C. Hyden-Granskog Impact of elective single embryo transfer on the twin pregnancy rate Hum. Reprod., July 1, 2003; 18(7): 1449 - 1453. [Abstract] [Full Text] [PDF]
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R. D. Lambert Safety issues in assisted reproduction technology: The children of assisted reproduction confront the responsible conduct of assisted reproductive technologies Hum. Reprod., December 1, 2002; 17(12): 3011 - 3015. [Abstract] [Full Text] [PDF]
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P. De Sutter, J. Gerris, and M. Dhont A health-economic decision-analytic model comparing double with single embryo transfer in IVF/ICSI Hum. Reprod., November 1, 2002; 17(11): 2891 - 2896. [Abstract] [Full Text] [PDF]
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L. Engmann, N. Maconochie, S. L. Tan, and J. Bekir Trends in the incidence of births and multiple births and the factors that determine the probability of multiple birth after IVF treatment Hum. Reprod., December 1, 2001; 16(12): 2598 - 2605. [Abstract] [Full Text] [PDF]
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