Human Reproduction, Vol. 14, No. 8, 1979-1982,
August 1999
© 1999 European Society of Human Reproduction and Embryology
Colour Doppler indices of follicular blood flow as predictors of pregnancy after in-vitro fertilization and embryo transfer
The Center for Human Reproduction, 750 N. Orleans Street, Chicago, IL 60610, USA
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Abstract |
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Peak systolic velocity (PSV) of individual follicles has been correlated with oocyte recovery, fertilization rate and embryo quality [in women undergoing in-vitro fertilization (IVF) and embryo transfer]. The present study assessed the role of quantitative and qualitative indices of follicular vascularity in predicting pregnancy after IVF and embryo transfer. A total of 106 women undergoing IVF treatment for infertility who were considered to be at risk of failure (>37 years of age, history of low response to gonadotrophin stimulation, or multiple failed IVF cycles) constituted the study group. PSV was measured from the three largest follicles on both the right and left ovaries on the day of human chorionic gonadotrophin (HCG) administration using an Acuson Sequoia with a 4–8 MHz transvaginal probe. The quality of follicular flow was graded from 1 to 4 according to the amount of visible colour flow around the follicle (grade 1 when one-quarter of the follicle, grade 2 when one-half, grade 3 when three-quarters, and grade 4 when the entire follicle was surrounded by colour). Clinical pregnancies resulted in 11 (10%) of the 106 high-risk women. Women who had PSV
10 cm/s in at least one follicle on the day of HCG administration more often became pregnant than those with PSV <10 cm/s (P = 0.05). All pregnancies occurred in women with grade 3 or 4 follicular blood flow. Qualitative as well as quantitative measurements of follicular flow predict pregnancy after IVF and embryo transfer.
Key words: colour Doppler/embryo transfer/follicular blood flow/in-vitro fertilization
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Introduction |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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Despite advances in reproductive technology, a need for introduction of procedures that will improve the efficacy, and thus reduce the cost, of treating infertile couples by in-vitro fertilization (IVF) and embryo transfer remains. Although many factors contribute to success in IVF programmes, a major role in determining delivery rate is played by the quality of oocytes retrieved (Sauer et al., 1992
). Transvaginal ultrasonography with colour and pulsed Doppler ultrasound has enabled the assessment of vascular changes in the ovary during the menstrual cycle (Bourne et al., 1991; Collins et al., 1991; Campbell et al., 1993; Kupesic and Kurjak 1993; Sladkevicius et al., 1993; Dickey, 1997). During spontaneously ovulating cycles, an increase in the maximum peak systolic velocity (PSV) in vessels supplying the dominant follicle has been documented (Bourne et al., 1991; Collins et al., 1991; Campbell et al., 1993; Kupesic and Kurjak 1993; Dickey, 1997). PSV of individual follicles among women undergoing IVF has been shown to be correlated with oocyte recovery (Nargund et al., 1996a,b; Oyesanya et al., 1996), fertilization rate (Nargund et al., 1996a), developmental potential of the oocyte (Van Blerkom et al., 1997) and quality of the preimplantation embryo (Nargund et al., 1996a; Oyesanya et al., 1996; Chui et al., 1997). A preliminary study (Chui et al., 1997) using qualitative assessment of follicular flow suggested that high-grade follicular vascularity is associated with increased pregnancy rate. The aim of the present study is to define the role of quantitative measurements of follicular blood flow in predicting pregnancy following IVF and embryo transfer. |
Materials and methods |
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Patients
A total of 106 women undergoing IVF treatment for infertility between April 5, 1997, and January 1, 1998, who were considered by their reproductive endocrinologist to be at increased risk for treatment failure, constituted the study group. Inclusion criteria for consideration of increased risk for treatment failure were as follows: age >37 years, history of low response to gonadotrophin stimulation, and previous IVF failure. A history of low response to gonadotrophin stimulation was diagnosed during human chorionic gonadotrophin (HCG) administration, in a previous IVF cycle, when there were fewer than four follicles between 12 and 22 mm (mean value of two diameters) or when the serum oestradiol concentration, drawn between 6 a.m. and 8 a.m., was <500 pg/ml (1836 SI units). Multiple IVF failures were arbitrarily defined as more than two previous IVF attempts without successful pregnancy.
Treatment regimens for ovarian stimulation were determined by the referring reproductive endocrinologist (n = 9) and were based on the woman's age and previous response to treatment. Treatment regimens included standard protocols and stop lupron protocols. The standard treatment protocol utilized luteal long-acting gonadotrophin-releasing hormone agonist (GnRHa; TAP Pharmaceuticals Inc.; Deerfield, IL, USA) down-regulation followed by gonadotrophin stimulation. The standard protocol initiated gonadotrophin therapy with 300 IU of follicle stimulating hormone (FSH) (Serono Laboratories; Randolph, MA, USA) per day in a split dose. The patients who had responded inadequately to the standard protocol in an earlier cycle initiated their gonadotrophin stimulation with either 450 IU FSH per day or 600 IU FSH per day in split doses. For some patients, the long-acting GnRHa was stopped after menses and then gonadotrophin stimulation was begun (stop lupron protocol). IVF was performed in the usual way using conscious i.v. sedation for an ultrasound-guided vaginal oocyte retrieval. Embryo transfer was performed vaginally on the second day after retrieval (day 0 was day of retrieval). Embryos were assigned a subjective quality score patterned after Veeck (1988), with 1 being a very poor quality, non-viable embryo and 5 being of optimal quality. The number of clinical pregnancies (gestational sac visible on transvaginal ultrasound at 3 weeks after embryo transfer) was recorded. A successful IVF cycle was defined as documentation of clinical pregnancy.
Colour Doppler imaging
Transvaginal colour Doppler imaging and pulsed Doppler spectral analysis were performed on the day of, but prior to, HCG administration. All scans were performed using an Acuson Sequoia (Acuson, Mountain View, CA, USA) with a 4–8 MHz transvaginal probe. Spectral analysis was performed using colour Doppler mapping on the three largest follicles from each of the right and left ovaries. The largest follicles were determined by the average of the maximum transverse and anteroposterior diameters. The spatial peak temporal average intensity for B-mode and colour Doppler imaging was <80 mW/cm2, which is within the safety limits recommended by the Bioeffects Committee of the American Institute of Ultrasound in Medicine (AIUM, 1993). The vascularity of each study follicle was graded from 1 to 4 according to the percentage of the follicular circumference in which flow was visible at the time of the scan. The grading system has been previously reported (Chui et al., 1997) and was as follows: grade 0 = no flow visible; grades 1, 2, 3 and 4 respectively had <25%, 26–50%, 51–75% and 76–100% of follicular circumference in which flow was identified. For all colour Doppler mapping, the following presets were held constant: spatial time resolution, S1; edge, –1; persistence, 2; post-processing, V:2; gate size, 1; and filter, 1. Scale was set at 0.025 m/s.
Spectral analysis was performed with the filter set under 50 Hz and sample volume range of 1.0–1.2 mm2. Flow velocity waveforms were used to calculate the highest PSV. The angle of the probe was adjusted until a flow velocity waveform with the maximum peak systolic shifted frequency was obtained and the value recorded.
Experimental design and statistical analysis
Women undergoing IVF for treatment of infertility had quantitative and qualitative indices of follicular vascularity obtained on the day of HCG administration. PSV was measured and quality of flow was graded from the three largest follicles on both the right and left ovaries. Mean PSV of follicular flow were compared between women experiencing clinical pregnancies and those that did not cycle using an unpaired Student's t-test. Previous studies had indicated that a follicle with a PSV 10 cm/s had a 70% chance of producing a good quality embryo compared to a 14% chance if PSV was <10 cm/s (Nargund et al., 1996a,b). We therefore compared clinical pregnancy rates among women possessing at least one follicle demonstrating a PSV 10 cm/s and grade 3–4 pattern of flow with those who did not, using Fisher's exact test. For continuous variables (Table I), a logit regression was performed to compare pregnant and non-pregnant patients. P < 0.05 was regarded as significant.
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Results |
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A total of 106 women aged 26–42 years undergoing 114 cycles of IVF for treatment of infertility had 565 follicles studied using colour Doppler flow. All the women were considered to be at risk for treatment failure for the following reasons: age >37 years (n = 35, 33%), history of low response to gonadotrophin stimulation (n = 43, 41%) and history of IVF failure (n = 62, 59%). Some women had more than one of the above criteria; hence, the sum of the percentages totals more than 100%. Clinical pregnancies resulted in 11 (10%) of the 106 high-risk women. Eight (73%) of the pregnancies ended in delivery of healthy infants and three (27%) aborted.
Of the 565 follicles studied, five were grade 0, 87 were grade 1, 138 were grade 2, 194 were grade 3, and 141 were grade 4. The results demonstrated that follicular vascularity grading was independent of follicular size. All pregnancies occurred in women with grade 3 or 4 follicular blood flow.
When women who conceived were compared with those who did not, no significant differences in mean age, number of days of stimulation, or follicular PSV were observed (Table I
). Women who subsequently became pregnant had a greater number of oocytes retrieved and embryos transferred than women who did not become pregnant. Women who received four or more embryos per transfer had a significantly higher pregnancy rate than those who had fewer than four embryos transferred (33 versus 3%, P = 0.002). However, if fewer than four follicles were measured for PSV, the rate of pregnancy in that cycle was the same as for four or more follicles measured, i.e. if at least one follicle had a PSV 10 cm/s and was grade 3–4 (P = 0.1) (Table II).
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The number of follicles with grade 3–4 flow within individual patients is compared with pregnancy rates for those cycles in Table III
. Pregnancy rate among women with one, two, three, four, five and six follicles classified as grade 3–4 was similar. The association between maximum follicular PSV and subsequent pregnancy in that cycle is shown in Table IV. Among the 11 pregnancy cycles, 10 (91%) had a threshold value of grade 3–4 flow with PSV 10 cm/s in at least one follicle. Thus, a threshold value of 10 cm/s for PSV in at least one follicle with grade 3–4 flow detected 91% of pregnancies with a false positive rate of 9%. There was a 15% (10/67) chance of clinical pregnancy per patient [13% (10/76) per cycle] in this high-risk population if the maximum follicular PSV was 0 cm/s as compared to 3% if the maximum follicular PSV was <10 cm/s (P = 0.05). A threshold value of 10 cm/s for PSV in at least one grade 3–4 follicle predicted a pregnancy with a sensitivity of 91%, specificity of 36%, positive predictive value of 13%, and negative predictive value of 97%.
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Discussion |
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Analysis of results from the present study demonstrates a direct relationship between establishment of clinical pregnancy after IVF and embryo transfer and follicular blood flow expressed by values of PSV. A previous study showed that follicular vascularity measured by qualitative grading predicted pregnancy after IVF and embryo transfer (Chui et al., 1997
). In that study (Chui et al., 1997), pregnancies were confined to women whose embryos were derived from follicles exhibiting grade 3 and 4 vascularity and with pregnancy rates per embryo transfer of 12.5 and 61.5% respectively. The present study confirmed the previous finding of a relationship between pregnancy and qualitative grading of follicular vascularity and extended the observation to include quantitative measurements of follicular blood flow. All pregnancies occurred in women with grade 3 and 4 follicular vascularity and 91% of pregnancies occurred with follicular PSV 10 cm/s. Women who had at least one follicle with a PSV of 10 cm/s at the time of HCG administration had a significantly higher pregnancy rate than women with maximum follicular PSV <10 cm/s. A threshold value of PSV 10 cm/s predicted pregnancy with high sensitivity (91%) and negative predictive value (97%), but low specificity (36%) and positive predictive value (13%), suggesting that reasons not associated with follicular flow are associated with lack of pregnancy in this high-risk population. However, even in a population at high risk for IVF failure, women with follicular flow of PSV 10 cm/s and grade 3–4 had a 13% pregnancy rate that cycle (Table IV). This finding is consistent with previous studies (Nargund et al., 1996a,b) that reported a significant relationship between follicular PSV within a given follicle and the recovery of an oocyte and the subsequent production of an embryo. The probability of producing a high-grade embryo was 75% if the follicular PSV was 10 cm/s (Nargund et al., 1996b). Transfer of high-grade embryos has been associated with higher pregnancy rates than transfer of low-grade embryos (Staessen et al., 1992).
The potential role of colour Doppler imaging in the overall assessment of folliculogenesis in women undergoing IVF and embryo transfer has been controversial (Dickey, 1997). Previous studies have involved the use of mean values for the PSV from many follicles (Balakier and Stronnell, 1994), the maximum PSV from serial monitoring (Tekay et al., 1995) and the PSV from individual follicles (Nargund et al., 1996a,b). When mean values for follicular PSV (Balakier and Stronnell, 1994) and maximum PSV from serial monitoring (Tekay et al., 1995) were evaluated, no differences in values between conception and non-conception cycles were noted. However, when individual follicles, oocytes, and preimplantation embryos were studied, a significant difference in PSV was found in conception compared with non-conception cycles. Thus, the discrepant findings can be explained by the experimental designs. The studies that minimize the between-follicle differences (Balakier and Stronnell, 1994; Tekay et al., 1995) yield no-difference results and those that detailed individual follicles showed significant results (Nargund et al., 1996a,b). In fact, in the present study and in the studies of individual follicles, no differences in mean value of follicular PSV were observed between women conceiving and those who did not. Thus, it is the individual follicle(s)/oocyte(s), not the cohort, that determines successful outcome. While it is true that the more follicles/oocytes available, the higher the probability that one of these will have the developmental potential to generate a viable pregnancy, it also holds true that if only one follicle possessing the developmental potential is available, the probability of pregnancy approaches 100%. The concept of quality rather than quantity is further emphasized when the number of follicles with grade 3–4 flow in an individual was compared to pregnancy rates that cycle (Table III). Pregnancy rates were similar in cycles with at least one follicle demonstrating grade 3–4 flow and in cycles with six follicles. Even in women who had fewer than four follicles measured at the time of HCG administration, 33% (3/9) became pregnant in that cycle if at least one grade 3–4 follicle had a PSV 10 cm/s (Table II). The key is to be able to identify follicles that hold the potential to generate viable pregnancies.
Developmental competence of a human oocyte is heterogeneous within cohorts of human oocytes. This fact is demonstrated most clearly by IVF programmes in which apparently normal metaphase II (MII)-stage oocytes resist penetration by competent spermatozoa (Bedford and Kim, 1993), fail to progress after penetration (Asch et al., 1995), or arrest development during the preimplantation stages (Edwards, 1986; Osborn and Moor, 1988; Van Blerkom, 1993; Van Blerkom et al., 1994). Metabolic differences between morphologically equivalent MII-stage oocytes have been reported and include oxygen consumption and ATP content (Magnusson et al., 1986; Van Blerkom, 1993). In addition, follicular fluid concentrations of oxygen (Gosden and Byat-Smith, 1986; Fischer et al., 1992; Van Blerkom, 1996; Van Blerkom et al., 1997) and vascular endothelial growth factor (Van Blerkom et al., 1997) have been associated with the developmental competence of the corresponding oocyte. The dissolved oxygen content of the follicle has been shown to be related to colour Doppler qualitative patterns (Van Blerkom et al., 1997). The current findings of an association between follicular PSV and subsequent clinical pregnancy are consistent with the hypothesis that follicular blood flow may be associated with events essential for successful reproduction. The mechanisms controlling follicular blood flow are unknown as is the link between vascularity and pregnancy. Whatever the mechanisms, the implications in IVF programmes are far reaching.
The knowledge gained from our study may have use in future management of women undergoing IVF and embryo transfer treatment. Pregnancy rates would be expected to be increased by selecting for transfer of embryos derived from follicles with PSV 10 cm/s. Conversely, pregnancy rates would be expected to decrease in cycles where the follicular PSV are universally poor. It may be appropriate to counsel these women as to the advisability of proceeding with oocyte retrieval. The net effect of the above actions is an increased pregnancy rate per embryo transfer. Currently, improved pregnancy rates after IVF and embryo transfer have come at a cost of an increased frequency of higher order gestations (Faber, 1997). If embryos with high developmental competence can be identified and transferred, then a small number of such replaced embryos will not reduce pregnancy rates, but rather the probability of multiple gestations. Prospective clinical trials are necessary to test these hypotheses.
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Notes |
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1 To whom correspondence should be addressed
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References |
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Submitted on January 5, 1999; accepted on May 11, 1999.
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