1 Abteilung für Pränatale Diagnostik und Therapie, Frauenklinik der Universität, Sigmund Freud Strasse 25, 53105 Bonn, Germany, 2 Abteilung für Reproduktionsmedizin und Endokrinologie, Frauenklinik der Universität, and 3 Institut für Medizinische Statistik, Universität Bonn, Germany
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Abstract |
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Key words: IVF/pregnancy rate/quantitative assessment/sub- endometrial blood flow/3D-ultrasound
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Introduction |
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Materials and methods |
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FI = weighted colour values/colour values, and
VFI = weighted colour values/(total voxels background values).
Endometrial thickness and volume were measured as described previously (Schild et al., 1999). Uterine artery blood flow was assessed by colour Doppler and the mean pulsatility index (PI) and peak systolic velocity (PSV) of the right and left uterine arteries were calculated. All measurements were corrected for the insonation angle. In no case was the angle >40°.
Subsequent to the ultrasound examination, ovarian stimulation with recombinant follicle stimulating hormone (rFSH) (Puregon®; Organon, Oberschleißheim, Germany) in appropriate doses was commenced. All patients underwent serial ultrasound examinations to assess follicular growth until at least three follicles with a mean diameter of 18 mm were seen. At this stage 10 000 IU of human chorionic gonadotrophin (HCG) (Pregnesin®; Serono, Unterschleißheim, Germany) were used to induce ovulation. Oocytes were collected by transvaginal ultrasound-directed follicular aspiration and up to three good quality embryos were transferred 48 h after oocyte retrieval. The number of blastomeres and morphological grade of each embryo were recorded. Progesterone vaginal suppositories (400 mg daily) were prescribed for 14 days as luteal support. Pregnancy was defined as the occurrence of a positive ß-HCG (>10 IU) value at day 12 after embryo transfer and a second, higher value 2 days later. Only pregnancies reaching HCG values >100 IU were considered for evaluation.
Statistical analysis
All data were analysed using the SPSS statistical package on a personal computer. Pearson's correlation coefficient, Student's two-tailed t-test and the MannWhitney U-test were used as appropriate. The correlation coefficient was tested for deviation from zero. Logistic regression analysis was performed with IVF outcome and the 3D indices being the independent and dependent variables respectively.
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Results |
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Intra-observer variability of the 3D indices was checked in 14 patients, the results demonstrating a high level of agreement (Table I). Since there was no significant difference in PI and PSV values between the right and left uterine artery, the mean value was calculated and used for subsequent analysis.
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Discussion |
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Achiron et al. (1995) evaluated the endometrial blood flow response to hormone replacement therapy in women with premature ovarian failure who planned to enter an oocyte donation programme. The authors examined 18 women with ovarian failure in the study group and 12 volunteers with normal menstrual cycles in the control group. With the exception of the early follicular phase no significant difference was revealed between the two groups. Endometrial blood flow increased during the proliferative stage of the cycle because of reduced downstream impedance manifested by increased diastolic flow. From the point of maximum oestradiol concentration, rising diastolic impedance resulted in decreased flow to the endometrium in the secretory phase (Achiron et al., 1995).
Zaidi et al. (1995) examined endometrial thickness, morphology, vascular penetration and velocimetry on the day of HCG administration in an IVF programme. Between conception and non-conception cycles there was no significant difference with regard to endometrial thickness, endometrial pattern, subendometrial PSV or subendometrial PI. Failure of implantation was associated with absent subendometrial blood flow. This was deemed a useful predictor of adverse IVF outcome (Zaidi et al., 1995).
A new concept of evaluating uterine receptivity by means of a uterine score including assessment of endometrial blood flow within zone 3 was introduced by Applebaum (1995). With absent endometrial blood flow, despite maximum values for the other parameters, no conception was achieved (Applebaum, 1995).
A similar concept was pursued by Salle et al. (1998) who proposed a uterine score calculated in the secretory phase of the menstrual cycle preceding IVF. Among other parameters, the presence or absence of colour in the subendometrial region was determined. The vascularization was considered as positive if more than three vessels penetrating the outer hypoechogenic area surrounding the endometrium could be seen. None of the individual ultrasonographic or Doppler parameters tested were of sufficient accuracy to predict uterine receptivity, whereas the uterine score seemed to be a useful predictor of implantation (Salle et al., 1998).
Bourne et al. (1996) defined subendometrial blood flow arbitrarily as waveforms emanating from an area 3.0 mm from the apparent basal layer of the endometrium. In their study of vascular and morphological changes in the human uterus after a positve self-test for the urinary luteinizing hormone (LH) surge, the authors reached the conclusion that the PSV and the time-averaged maximum velocity (TAMXV) were the most sensitive markers of physiological function for small vessels, e.g. the subendometrial spiral arteries, whereas an index of impedance appeared to be more appropriate for large vessels, e.g. the uterine arteries (Bourne et al., 1996
).
Conflicting results of uterine artery blood flow assessment at the beginning of ovarian stimulation have been described. In the study of Bloechle et al. (1997) conception cycles were characterized by significantly lower PI and resistance index (RI) values in the ascendent uterine artery at the beginning of ovarian stimulation. In contrast, our data did not reveal any correlation between uterine artery Doppler findings at stimulation induction and subsequent pregnancy rate.
Battaglia et al. (1997) studied thromboxane production and colour Doppler changes in women undergoing different ovarian stimulation protocols. Thromboxane concentrations were measured on blood samples taken at the beginning of ovarian stimulation and on the day of oocyte retrieval. Thromboxane production was also evaluated on endometrial cells sampled and cultured on the day of ovum retrieval. Significantly lower endometrial culture cell thromboxane values were observed in conception cycles while plasma thromboxane concentrations were not significantly different between conception and non-conception cycles. The Doppler PI values of uterine and spiral arteries on the day of oocyte retrieval were significantly lower in women achieving pregnancy. In this group the presence and endometrial penetration of spiral arteries appeared to be more intense although this subjective impression could not be quantified (Battaglia et al., 1997). In our opinion, this obvious lack of quantitative assessment cannot provide firm evidence that endometrial vascularity is indeed increased in conception cycles.
Recently, Yuval et al. (1999) examined whether endometrial blood flow and thickness could predict the success of IVF. In their study of 156 cycles, the authors assessed the endometrial PI and RI, the systolic/diastolic ratio and endometrial thickness on the day of oocyte retrieval and on the day of embryo transfer. Neither endometrial thickness nor endometrial blood flow appeared to be correlated with pregnancy rate (Yuval et al., 1999).
In our study, no significant difference was found between the pregnant and non-pregnant group with regard to serum oestradiol concentrations, endometrial thickness and volume. However, significantly lower 3D indices were observed in conception cycles compared with non-conception cycles, suggesting that a lesser degree of intrauterine vascularization and perfusion at the beginning of ovarian stimulation indicated a more favourable endometrial milieu. These results were rather surprising, as the opposite might have been expected. Possibly, a better functional down-regulation of the endometrium following GnRH agonist application for 1214 days, as expressed by lower 3D indices, increases the chances of successful implantation. This hypothesis, however, will need to be tested in further studies.
Previous work on the microvasculature in the endometrium throughout the normal menstrual cycle has demonstrated that the capillary basal lamina is loosely formed and discontinuous in the early proliferative phase. Progressive but heterogeneous differentiation of the endothelial cells occurs towards the mid-secretory phase of the cycle. It seems plausible that the co-ordinated growth and development of the endometrium is supported by extensive physical contacts connecting its component cell types (Roberts et al., 1992). These findings demonstrate the variable nature of the endometrial vessel system and suggest that specific alterations may be necessary in preparation for embryo implantation. In a review on the structure and function of endometrial blood vessels (Rogers, 1996
), it was confirmed that endometrial blood vessels form a vascular bed with unusual properties in that these vessels undergo constant cycles of growth and regression during the reproductive life of the woman (Rogers, 1996
).
In conclusion, at the initiation of ovarian stimulation following GnRH down-regulation, significant differences in (sub-) endometrial blood flow and vessel density can be found between subsequently pregnant or non-pregnant women. These findings may allow earlier prediction of a non-receptive endometrium, at a time when further stimulation therapy could be postponed to a cycle with a more favourable endometrial milieu. Further studies are needed to evaluate whether this proposed management will result in a higher implantation rate.
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Notes |
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References |
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Submitted on June 9, 1999; accepted on October 7, 1999.