Hum. Reprod. Advance Access published online on December 5, 2006
Human Reproduction, doi:10.1093/humrep/del458
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© The Author 2006. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Endometrial and subendometrial vascularity is higher in pregnant patients with livebirth following ART than in those who suffer a miscarriage
Department of Obstetrics and Gynaecology, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China
1 To whom correspondence should be addressed at: Department of Obstetrics and Gynaecology, The University of Hong Kong, 6/F, Professorial Block, Queen Mary Hospital, Pokfulam Road, Hong Kong. Tel: +86 852 28553400; Fax: +86 852-28175374; E-mail: nghye{at}hkucc.hku.hk
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Abstract |
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BACKGROUND: Blood flow towards the peri-implantation endometrium may have effects on miscarriage and live birth following assisted reproduction treatment, in addition to its role in implantation.
METHODS: Three-dimensional ultrasound examination with power Doppler was performed on the day of oocyte retrieval in stimulated IVF cycles and on LH+1 day in frozen thawed-embryo transfer (FET) cycles to measure endometrial thickness, endometrial pattern, uterine artery Doppler flow indices, endometrial volume, vascularization index (VI), flow index (FI), vascularization flow index (VFI) of endometrial and subendometrial regions.
RESULTS: In stimulated IVF cycles, 45 (28.0%) out of 161 pregnant patients subsequently miscarried. Patients in the live birth group had significantly higher endometrial VI and VFI and subendometrial VI, FI and VFI, when compared with those in the miscarriage group. In a multiple logistic regression analysis, only endometrial VI was significantly associated with the chance of live birth with an odds ratio of 1.384 [95% confidence interval (CI) 1.025–1.869, P=0.034]. For FET cycles, patients in the live birth group had significantly higher endometrial VFI, subendometrial VI and VFI than those in the miscarriage group.
CONCLUSIONS: Endometrial and subendometrial vascularity was significantly higher in pregnant patients with live birth following stimulated IVF and FET treatment than in those who suffered a miscarriage.
Key words: endometrial and subendometrial vascularity/live birth/miscarriage/3D power Doppler
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Introduction |
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Successful implantation depends on a close interaction between the blastocyst and the receptive endometrium. A good blood supply towards the peri-implantation endometrium is usually considered to be an essential requirement for normal implantation. Gannon et al. (1997)
used an intrauterine laser Doppler technique to measure endometrial microvascular blood flow, which differed between phases of the menstrual cycle with significant increase in blood flow during early follicular and early luteal phases. Endometrial microvascular blood flow which is determined by an intrauterine laser Doppler technique in the early luteal phase of the cycle preceding an IVF cycle has been shown to be predictive of pregnancy and superior to other conventional parameters predicting endometrial receptivity (Jinno et al., 2001).
In combination with three-dimensional (3D) ultrasound, power Doppler provides a unique non-invasive tool with which to examine the blood supply towards the whole endometrium and the subendometrial region (Schild et al., 2000; Kupesic et al., 2001; Wu et al., 2003; Raine-Fenning et al., 2004; Ng et al., 2004a, 2004b, 2005). Significantly higher subendometrial vascularity was shown in pregnant IVF cycles (Kupesic et al., 2001; Wu et al., 2003). However, we demonstrated that endometrial vascularity was significantly lower in the pregnant group than in the non-pregnant group in stimulated IVF/embryo transfer (ET) cycles (Ng et al., 2006a). Endometrial and subendometrial vascularity was similar between pregnant and non-pregnant patients in frozen-thawed dembryo transfer (FET) cycles (Ng et al., 2006b).
Angiogenesis plays a critical role in various female reproductive processes such as development of a dominant follicle, formation of a corpus lutuem, growth of endometrium, implantation and development of the placenta (Abulafia and Sherer, 2000; Smith, 2001). It is possible that blood flow towards the peri-implantation endometrium may have effects on the miscarriage and live birth following assisted reproduction treatment (ART), in addition to its role in implantation. There is little information in the literature addressing the impact of the endometrial and subendometrial vascularity on the pregnancy loss following IVF and FET treatment. Isaksson et al. (2000) showed that uterine artery pulsatility index (PI) and resistance index (RI) on the day of ET were unrelated to the risk of the pregnancy ending in spontaneous miscarriage or ectopic pregnancy.
The aim of this prospective observational study was to compare the endometrial and subendometrial vascularity as measured by 3D power Doppler ultrasound between pregnant patients with miscarriage and live birth following stimulated IVF and FET cycles. The hypothesis was that the endometrial and subendometrial vascularity would be significantly higher in pregnant patients with live birth than those with miscarriage because a good blood supply towards the endometrium is usually considered as an essential requirement for implantation (Gannon et al., 1997; Jinno et al., 2001).
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Materials and methods |
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Infertile patients attending the Assisted Reproduction Unit of the Department of Obstetrics and Gynecology, The University of Hong Kong, between November 2002 and April 2005 for stimulated IVF or FET treatment were recruited. Exclusion criteria were: (i) history of recurrent miscarriage, i.e. three consecutive spontaneous miscarriages, (ii) distortion of the uterine cavity shown on scanning and (iii) ectopic pregnancy following IVF or FET treatment. The indications of IVF included tubal, male, endometriosis, unexplained and mixed factors. Serum basal FSH concentration was checked on Days 2–3 of the cycle within 2–3 months of commencing treatment. Women with polycystic ovary syndrome (PCOS) were diagnosed if they had irregular long menstrual cycles (>35 days) and the presence of 12 or more antral follicles on transvaginal scanning (The Rotterdam ESHRE/ASRM-Sponsored PCOS Consensus Workshop Group, 2004
). All patients recruited in this study did not have any history of hysteroscopic metroplasty, removal of submucous fibroids or lysis of intrauterine adhesion. Every patient gave a written informed consent prior to participating in the study, which was approved by the Ethics Committee, Faculty of Medicine, the University of Hong Kong. They were evaluated only once during the study period and did not receive any monetary compensation for their participation in the study.
Stimulated IVF cycles
All patients received a long protocol of pituitary down-regulation as previously described (Ng et al., 2000). In short, all women were pretreated with buserelin (Suprecur, Hoechst, Frankfurt, Germany) nasal spray 150 µg four times a day from the midluteal phase of the cycle preceding the treatment cycle and received human menopausal gonadotrophin (hMG), (Pergonal, Serono, Geneva, Switzerland) for ovarian stimulation. Human chorionic gonadotrophin (hCG) (Profasi, Serono, Geneva, Switzerland) was given intramuscularly when the leading follicle reached 18 mm in diameter and there were at least three follicles of 
16 mm in diameter. Serum estradiol (E2) concentration was measured on the day of hCG administration. Transvaginal ultrasound-guided oocyte retrieval (TUGOR) was scheduled 36 h after the hCG injection.
Patients were advised to have not more than two embryos replaced into the uterine cavity 2 days after TUGOR but replacing three embryos was allowed after counselling of the risk of multiple pregnancy. Excess good quality embryos were frozen on the day of ET for subsequent transfer if the patient did not conceive in that cycle. Immediately before the transfer or cryopreservation, embryos were examined for the number/regularity of blastomeres and the degree of fragmentation. Embryos were graded according to the following criteria: Grade 1: blastomeres of equal size, no cytoplasmic fragments; Grade 2: blastomeres of equal size, minor (<25%) cytoplasmic fragments; Grade 3: blastomeres of distinctly unequal size, no cytoplasmic fragments; Grade 4: blastomeres of distinctly unequal size, minor cytoplasmic fragments; Grade 5: blastomeres of equal or unequal size, major cytoplasmic fragments and Grade 6: few or no recognized blastomeres, major cytoplasmic fragments. Grades 5 and 6 embryos were discarded because of poor quality.
FET cycles
Those who did not get pregnant in the stimulated IVF cycle and had two or more frozen embryos underwent FET in natural or clomiphene citrate -induced cycles, at least 2 months after the stimulated cycle. Patients having regular ovulatory cycles underwent FET in their natural cycles. Clomiphene Citrate (Clomid, Merrell, Staines, UK) 50–150 mg was given daily for 5 days from Days 3–7 to patients with irregular long cycles or absence of serum E2 rise and an LH surge in previous natural cycles. They attended the clinic daily from 18 days before the next expected period for the determination of serum E2 and LH concentrations until the LH surge, which was defined as the day on which the LH level was above 20 IU/l and doubled the average of the LH levels over the past 3 days. FET was performed on the third day after the LH surge.
Frozen embryos were thawed on the day of FET at room temperature for 40 s and then at 30°C in a water -bath for 40 s. Subsequently, the cryoprotectant was removed by washing the embryos successively through phosphate buffers with decreasing concentration of propanediol and the embryos were cultured in the CO2 incubator for a short period before transfer. After thawing, frozen embryos were examined for the number/regularity of blastomeres and the degree of fragmentation and graded according to the earlier mentioned criteria. Any embryo with equal to or more than half of the number of blastomeres surviving was transferred.
Ultrasound markers of endometrial receptivity
The details of ultrasound measurement and 3D data analysis were as previously described (Ng et al., 2004). All ultrasound measurements were performed by EHYN on hCG +2 days (prior to TUGOR) in stimulated IVF cycles and LH+1 day in FET cycles using Voluson 730® (Kretz, Zipf, Austria) at around 8–10 am after they had emptied the bladder. The results of the ultrasound assessment did not affect subsequent clinical management. The maximum thickness of the endometrium on both sides of the midline was measured in a longitudinal plane. The endometrial pattern visualized was designated as a multilayered or a non-multilayered endometrium (Sher et al., 1991). A multilayered endometrium presented as a triple-line pattern in which hyperechogenic outer lines and a well-defined central echogenic line were seen with hypoechogenic or black areas between these lines. A non-multilayered endometrium consisted of homogenous endometrial patterns characterized by either hyperechogenic or isoechogenic endometrium.
Using colour Doppler in the 2D mode, flow velocity waveforms were obtained from the ascending main branch of the uterine artery on the right and left side of the cervix in a longitudinal plane before they entered the uterus. The gate of the Doppler was positioned when the vessel with good colour signals was identified on the screen. PI and RI of the uterine arteries were calculated electronically when similar consecutive waveforms of good quality were obtained (Ng and Ho, 2002). As there were no differences in uterine PI and RI between the left and the right sides, the averaged uterine PI and RI were given.
The ultrasound machine (Voluson 730) was switched to the 3D mode with power Doppler. The setting condition for this study was as follows: frequency=mid, dynamic set=2, balance=G>140, smooth=5/5, ensemble=12, line density=7 and power Doppler map=5. The setting condition for the subpower Doppler mode was as follows: gain=–6.0, balance=140, quality=normal, wall motion filter=low1 and velocity range=0.9 kHz. The resulting truncated sector covering the endometrial cavity in a longitudinal plane of the uterus was adjusted and moved, and the sweep angle was set to 90° to ensure that a complete uterine volume encompassing the entire subendometrium was obtained. The patient and the 3D transvaginal probe remained as still as possible during the volume acquisition. A 3D data set was then acquired using the medium-speed sweep mode. The resulting multiplanar display was examined to ensure that the area of interest was captured in its entirety. If the volume measurement was completed without a power Doppler artefact, the data set was stored for later analysis by EHYN.
The built-in VOCAL® (Virtual Organ Computer-Aided Analysis) Imaging Program for the 3D power Doppler histogram was used in the analysis, along with computer algorithms, to measure the endometrial volume and indices of blood flow within the endometrium. Vascularization index (VI), which measures the ratio of the number of colour voxels to the number of all the voxels, is thought to represent the presence of blood vessels (vascularity) in the endometrium, and this was expressed as a percentage (%) of the endometrial volume. Flow index (FI), the mean power Doppler signal intensity inside the endometrium, is thought to express the average intensity of flow. Vascularization flow index (VFI) is a combination of vascularity and flow intensity (Pairleitner et al., 1999). During analysis and calculation, the manual mode of the VOCAL Contour Editor was used to cover the whole 3D volume of the endometrium with a 15° rotation step. Hence, 12 contour planes were analysed for the endometrium of each patient to cover 180°.
Following the assessment of the endometrium itself, the subendometrium was examined through the application of ‘shell imaging’ which allows the user to generate a variable contour that parallels the originally defined surface contour. In the present study, the subendometrial region was considered to be within 1 mm of the originally defined myometrial–endometrial contour. The VI, FI and VFI of the subendometrial region were obtained accordingly.
Luteal phase was supported by two doses of hCG or vaginal progesterone (Cyclogest, Cox Pharmaceuticals, Barnstaple, UK). A urine pregnancy test was done 16 days after ET in stimulated IVF and FET cycles. If it was positive, ultrasound examination was performed 10–14 days later to confirm intrauterine pregnancy and to determine the number of gestational sacs present. Patients were referred for antenatal care around 10–12 weeks of gestation and informed us the outcome of the pregnancy after miscarriage or delivery. Biochemical pregnancy was considered when patients noticed vaginal bleeding shortly after a positive pregnancy test which became negative on subsequent testing or there was no evidence of an intrauterine sac on scanning with low serum hCG concentrations which were negative on serial monitoring. A clinical miscarriage was defined as the loss of an intrauterine pregnancy before 24 completed weeks of gestation, whereas a baby born after 24 weeks gestation was classified as live. The miscarriage group included patients with biochemical pregnancy and clinical miscarriage.
The intra-observer reliability was expressed as the mean intraclass correlation coefficient (ICC) with 95% CI. The mean ICC was 0.970 (95% CI: 0.920, 0.989) for endometrial thickness, 0.973 (95% CI: 0.912, 0.992) for PI and 0.951 (95% CI: 0.838, 0.985) for RI. The mean ICC for 3D scanning of endometrial volume, VI, FI and VFI were 0.9509 (95% CI: 0.8591, 0.9838), 0.9896 (95% CI: 0.9689, 0.9966), 0.8957 (95% CI: 0.7157, 0.9649) and 0.9916 (95% CI: 0.9750, 0.9973), respectively. The mean ICC for data acquisition of endometrial volume, VI, FI and VFI were 0.9923 (95% CI: 0.9746, 0.9917), 0.9827 (95% CI: 0.9437, 0.9949), 0.9884 (95% CI: 0.9619, 0.9966) and 0.9852 (95% CI: 0.9517, 0.9957), respectively.
Serum FSH and E2 concentrations were measured using commercially available kits (Automated Chemiluminescence System, Bay Corporation, NY, USA). The inter-assay and intra-assay coefficients of variation for serum FSH concentration were 2.8 and 1.7%, respectively. The intra- and inter-assay coefficients of variation for serum E2 concentration were 8.1 and 8.7%, respectively.
Statistical analysis
The primary outcome measure was the live birth. Continuous variables were not normally distributed and were given as median (interquartile range), unless indicated. Statistical analyses were carried out by Mann–Whitney U-tests, chi-square and Fisher's exact tests, whenever these were appropriate. Multiple logistic regression analysis and the receiver-operator characteristic (ROC) curve analysis were applied to determine the best predictive variables for live birth (Altman and Bland, 1994). The sensitivity, specificity, likelihood ratios and odds ratios (ORs) were determined. The likelihood ratio of a positive test result (LR+) indicates the likelihood of a positive test in a patient with the live birth over the likelihood of a positive test in a patient without the live birth. The likelihood ratio of a negative test result (LR–) indicates the likelihood of a negative test in a patient with the live birth over the likelihood of a negative test in a patient without the live birth. The LR+ is calculated as sensitivity/(1–specificity) and the LR– is calculated as (1–sensitivity)/specificity. An LR+ between 2 and 5 indicates a fair test, between 5 and 10 is good and >10 is excellent. A LR– between 0.5 and 0.2 indicates a fair test, between 0.2 and 0.1 is good and <0.1 is excellent. The OR is given by LR+/LR– and reflects the probability of a patient with a positive test having a live birth.
Statistical analysis was performed using the Statistical Program for Social Sciences (SPSS Inc., Version 13.0, Chicago, USA). The two-tailed value of P<0.05 was considered statistically significant.
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Results |
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Stimulated IVF cycles
During the study period, a total of 662 patients received ovarian stimulation for IVF treatment, with 645 patients proceeding to TUGOR. Cycle cancellation among 17 patients who had poor ovarian response resulted in their non-participation. Three patients declined to participate because of personal reasons. Six patients were not eligible, two patients had a history of recurrent miscarriage and four patients were found to have distortion of the uterine cavity due to either uterine fibroids (n=3) or a congenital uterine abnormality (n=1). ET was performed in 564 patients only and 162 (28.7%) patients had a positive pregnancy test. One patient developed ectopic pregnancy and was excluded from the final analysis.
Out of 161 patients with a positive pregnancy test, 45 (28.0%) patients subsequently miscarried: 18 (11.2%) due to biochemical pregnancy and 27 (16.8%) a clinical miscarriage. First and second trimester miscarriages were encountered in 24 and 3 patients, respectively. Two gestational sacs were observed in 2 (7.4%) of 27 patients with clinical miscarriage and in 33 (28.7%) of 116 patients with live birth (P=0.04, chi-square test).
Table I summarizes the demographic data and ovarian responses of the miscarriage and live birth groups. There were no significant differences in the age of women, the percentage of primary infertility, the duration of infertility, the cause of infertility, the number of previous miscarriages, the number of smokers, body mass index (BMI), basal serum FSH concentration, the number of PCOS women, hMG dosage and duration, serum E2 concentration, the number of oocytes obtained and the number of embryos replaced between the two groups. As multiple embryos were replaced in the majority of cycles, the embryo with the lowest grade was considered to be the best quality embryo. The blastomere numbers and grade of the best quality embryo were similar between the miscarriage and live birth groups (Table II).
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Patients in the live birth group had significantly higher endometrial VI and VFI and subendometrial VI, FI and VFI, when compared with those in the miscarriage group (Table III). Endometrial thickness, endometrial volume, endometrial pattern, uterine PI and RI and endometrial FI were similar between the miscarriage and live birth groups.
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When the age of women, the type of infertility, the duration of infertility, BMI, the number of oocytes obtained, serum E2 concentration, the number of embryos replaced, blastomeres number and grade of the best quality embryo, uterine PI, uterine RI, endometrial thickness, endometrial pattern, endometrial volume, 3D power Doppler indices of endometrial and subendometrial regions were entered in a conditional forward fashion in multiple logistic regression analysis, only endometrial VI was significantly associated with the chance of live birth with an OR of 1.384 (95% CI: 1.025–1.869, P=0.034). Other parameters were not predictive of live birth. The ROC curve analysis showed that endometrial VI and VFI and subendometrial VI and VFI had the area under the curve around 0.6 with 95% CI >0.5 (Table IV). The best prediction rate was achieved by an endometrial VI cut-off of >0.306, with a sensitivity of 80.7% and specificity of 42.9%. The positive LR+ratio LR–ratio and OR were 1.44, 0.45 and 3.2 (95% CI: 1.5–6.8), respectively (Figure 1).
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Endometrial vascularity was absent in 19 patients and subendometrial vascularity was absent in 18 patients. Fourteen patients had no endometrial and subendometrial vascularity. There was a trend of lower live birth rate in patients without endometrial and subendometrial vascularity than those with endometrial and subendometrial vascularity, although the difference did not reach statistical significance (Table V).
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Blastomere numbers and grade of the best quality embryo, endometrial thickness, endometrial volume, endometrial pattern, uterine PI and RI, 3D power Doppler indices of endometrial and subendometrial regions were similar between patients with biochemical pregnancy and clinical miscarriage (data not shown). All these parameters were also comparable for patients in the live birth group with one or two gestational sacs (data not shown).
FET cycles
A total of 193 women were recruited into the study during the study period. Frozen-thawed embryos were replaced in 164 natural and 29 clomiphene citrate-induced cycles. Fifty-six patients (29.0%) had a positive pregnancy test and 12 (21.4%) patients subsequently miscarried: 3 (5.4%) biochemical pregnancy and 9 (16.0%) clinical miscarriage. The live birth rate was similar in natural and clomiphene citrate-induced cycles (37/46 versus 7/10, P=0.433, Fisher's exact test). There were no significant differences in the age of women, the percentage of primary infertility, the duration of infertility, the cause of infertility, the number of previous miscarriages, the number of smokers, BMI, basal serum FSH concentration, ovarian responses of the stimulated cycles and the number of frozen embryos replaced between the miscarriage and live birth groups (data not shown). The blastomeres number and grade of the best quality embryo were also similar between the miscarriage and live birth groups (Table II).
Patients in the live birth group had significantly higher endometrial VFI, subendometrial VI and VFI when compared with those in the miscarriage group (Table VI). Endometrial thickness, endometrial volume, endometrial pattern, uterine PI and RI, endometrial VI and FI and subendometrial FI were comparable between the miscarriage and live birth groups.
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Discussion |
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Many studies have been conducted to evaluate the role of various ultrasound parameters in predicting pregnancy during ART (Turnbull et al., 1995
; Friedler et al., 1996; Dickey et al., 1997) but little information exists in the literature with regard to their role in predicting subsequent pregnancy outcomes. In 111 treatment cycles consisting of 82 stimulated IVF cycles and 29 FET cycles performed in 102 infertile women, Isaksson et al. (2000) showed that uterine Doppler flow indices on the day of ET were not related to the risk of pregnancy ending in spontaneous miscarriage or ectopic pregnancy. Although uterine Doppler flow indices were comparable in stimulated and natural cycles, endometrial and subendometrial vascularity was significantly different between stimulated and natural cycles (Ng et al., 2004b). Ectopic pregnancies should also be separated from those pregnancies ending in spontaneous miscarriage.
To the best of our knowledge, this is the first study addressing the role of the endometrial and subendometrial vascularity measured by 3D power Doppler ultrasound in the prediction of live birth following IVF and FET cycles. In the present study, we demonstrated that pregnant patients with live birth following stimulated IVF and FET treatment had significantly higher endometrial and subendometrial vascularity when compared with those with miscarriage. Other demographic characteristics and ovarian response parameters were comparable between these two groups. We confirmed the findings of Isaksson et al. (2000) that uterine Doppler flow indices on the day of TUGOR were not predictive of subsequent miscarriage or live birth.
Endometrial VI was the only factor predictive of live birth in a multiple logistic regression analysis. In the prediction of live birth, the area under the ROC curve for endometrial VI was 0.64 and the OR was 3.2 (95% CI: 1.5–6.8) with a cut-off of >0.306. This is probably related to the fact that at least 50% of the first trimester spontaneous miscarriages have an abnormal karyotype (Hassold, 1986). Patients with absent endometrial or subendometrial vascularity had a non-significant reduction in the live birth rate when compared with those with present endometrial or subendometrial vascularity. Despite significant differences in endometrial and subendometrial vascularity between stimulated and natural cycles (Ng et al., 2004b), significant differences in endometrial and subendometrial vascularity between pregnant patients with miscarriage and live birth were also demonstrated in FET cycles.
The results of the present study seemed to be contradictory to that of our previous one (Ng et al., 2006a), which showed that endometrial vascularity was significantly lower in the pregnant group than in the non-pregnant group in stimulated IVF cycles. During a normal menstrual cycle, Raine-Fenning et al. (2004) showed that endometrial and subendometrial vascularity by 3D ultrasound increased during the proliferative phase, peaking around 3 days prior to ovulation before decreasing to a nadir 5 days post-ovulation. Therefore, there is a period of relatively reduced perfusion in the immediate post-ovulatory period, extending to the implantation period in spontaneous cycles. It is proposed that the degree of change in endometrial perfusion from the late follicular phase through to the early luteal phase is a more important determinant of endometrial receptivity. Therefore, good blood flow towards the endometrium from the late follicular phase may have a role in the subsequent miscarriage or live birth, whereas the degree of change in endometrial perfusion from the late follicular phase through to the early luteal phase is a more important determinant of implantation. In order to predict pregnancy and live birth following IVF treatment, different timing of ultrasound examination may be required. Further longitudinal studies of endometrial and subendometrial vascularity in the late follicular phase and early luteal phase should be performed to evaluate its role in implantation and pregnancy loss.
Our patients did not have any history of hysteroscopic metroplasty, removal of submucous fibroids or lysis of intrauterine adhesion. Patients with history of recurrent miscarriage (Clifford et al., 1997) or distortion of the uterine cavity related to congenital uterine abnormalities (Woelfer et al., 2001) were excluded from this study because of a higher risk of miscarriage in subsequent pregnancies. We did not separate pregnant patients with biochemical pregnancy and clinical miscarriage as it is likely that these represent the continuum of a condition. There were also no differences in endometrial thickness, endometrial volume, endometrial pattern, uterine Doppler flow indices and 3D power Doppler indices of endometrial and subendometrial regions. It would be interesting to study the relationship between endometrial/subendometrial blood vascularity and other pregnancy complications such as pre-eclampsia and intrauterine growth retardation. However, many patients were not managed in our centre for the antenatal care and these complications could not be examined in the present study.
About 10–15% of clinically recognized pregnancies end in spontaneous miscarriage and there is an increasing risk of spontaneous miscarriage with maternal age (Nybo Andersen et al., 2000). High maternal age was a significant risk factor for spontaneous miscarriage irrespective of the number of previous miscarriages and parity. However, we could not demonstrate that age of women was a factor predictive of live birth in this study, probably because the majority of our patients were less than 40 years old. The spontaneous miscarriage rate among IVF and FET pregnancies was comparable to the rate arising from natural conceptions (Schieve et al., 2003). This suggests that IVF or FET treatment does not pose an increased risk for subsequent spontaneous miscarriage. Smoking and transferring poor quality embryos increased the early pregnancy loss in ART, whereas the age of women, obesity and the PCOS status were found to have no effect (Winter et al., 2002). The blastomere numbers and grade of the best quality embryo were similar for the miscarriage and live birth groups in the present study. The key concern of ART is the risk of multiple pregnancies which increase the risk of spontaneous miscarriage (Fauser et al., 2005). However, La Sala et al. (2004) did not identify a clear relationship between early spontaneous loss of multiple pregnancies and initial number of gestational sacs. Indeed, we observed a significantly higher percentage of twin pregnancies in pregnant patients with live birth, when compared with those with miscarriage.
Human placentation is more complex than that of other mammalian species including the higher primates, and abnormalities of placentation are associated with diseases such as miscarriage or pre-eclampsia (Jauniaux et al., 2005). There is substantial anatomical evidence that in the majority of cases the most common complications of pregnancy, i.e. spontaneous miscarriage and pre-eclampsia stem from a defect in early trophoblast invasion and a failure to convert the spiral arteries into low-resistance channels. In about two-thirds of early pregnancy failures, there is anatomical evidence of defective placentation, which is mainly characterized by a thinner and fragmented trophoblast shell, and reduced cytotrophoblast invasion of the lumen at the tips of the spiral arteries (Hustin et al., 1990). On the basis of our findings, it is tempting to postulate that a better endometrial and subendometrial vascularity can lead to a better placental development during pregnancy which is associated with a lower risk of miscarriage and a higher chance of live birth following ART.
Transvaginal scanning is essential in the management of early pregnancy complications such as threatened miscarriage. The ability of colour Doppler imaging to detect small vessels such as the terminal part of the uteroplacental circulation has given rise to much enthusiasm from clinicians interested in predicting early and late pregnancy complications related to an abnormal placentation. Overall, the predictive value of Doppler measurements of resistance to blood flow in early pregnancy is limited (Frates et al., 1996; Giacobbe et al., 2002; Pellizzari et al., 2002). Doppler studies in the first trimester have failed to demonstrate abnormal blood flow indices in the uteroplacental circulation of pregnancies that subsequently ended in miscarriage (Alcazar and Ruiz-Perez, 2000; Makikallio et al., 2001). That we observed no differences in uterine Doppler flow indices may be related to the fact that uterine artery blood flow is a poor reflection of subendometrial blood flow during stimulated and natural cycles and its measurement cannot reflect endometrial blood flow during stimulated cycles (Ng et al., 2006c). The uterine Doppler flow indices were, however, significantly higher in non-pregnant (Habara et al., 2002) and pregnant (Nakatsuka et al., 2003) women with recurrent miscarriage than the controls.
It may also be too late to detect abnormal uterine or endometrial blood flow indices in those pregnancies presenting as bleeding during pregnancy as there is no effective therapy to prevent miscarriage (Aleman et al., 2005). However, we can measure endometrial blood flow indices in IVF and FET treatment, even before the time of implantation. This may open up a possibility to start therapeutic measures to reduce the miscarriage in those patients who are found to have lower endometrial and subendometrial blood vascularity on the day of TUGOR. Therapeutic agents such as aspirin (Rubinstein et al., 1999) or sildenafil (Sher and Fisch, 2000) may improve the blood flow towards the endometrium. It is certainly too early to speculate whether these agents may work and prospective randomized studies should be performed to evaluate their effectiveness in reducing miscarriage.
In conclusion, endometrial and subendometrial vascularity measured by 3D power Doppler ultrasound was significantly higher in pregnant patients with live birth following stimulated IVF and FET treatment than in patients who suffered a miscarriage.
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Acknowledgments |
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This study was funded by the Hong Kong Research Grant Council (HKU 7280/01M).
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References |
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Submitted on July 24, 2006; resubmitted on October 25, 2006; accepted on October 31, 2006.
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