1 Department of Obstetrics and Gynaecology, 2 Department of Diagnostic Radiology and 3 Department of Anatomy, Queen Mary Hospital, The University of Hong Kong, Pokfulam, Hong Kong
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Abstract |
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Key words: Doppler haemodynamics/endometrial perfusion/high responders/luteal phase/ovarian stimulation syndrome
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Introduction |
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Materials and methods |
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All women were stimulated with the departmental standard protocol of ovarian stimulation (Basir et al., 2001) for IVF and embryo transfer. These women were pre-treated with a gonadotrophinreleasing hormone (GnRH) analogue, buserelin (Suprecur®; Hoechst, Frankfurt, Germany) nasal spray 150 µg four times a day from the mid-luteal phase of the cycle preceding the treatment cycle. Baseline transvaginal ultrasound scanning was performed on the second day of the cycle to assess uterine and ovarian morphology and to confirm pituitary down-regulation. Assay of serum oestradiol was also performed on the second day of the cycle. Human menopausal gonadotrophin (HMG, 75 IU FSH and LH; Pergonal®; Serono, Switzerland) injections were then started. The women underwent monitoring of ovarian response by assay of serum oestradiol concentrations and serial transvaginal ultrasonographic scans during the follicular phase. Human chorionic gonadotrophin (HCG, Pregnyl®; Organon, Oss, The Netherlands) 10 000 IU was given i.m. when the mean diameter of the leading follicle was >18 mm and there were at least three follicles with a mean diameter of
16 mm. The day of HCG administration (day 0) was used as the reference for determining the cycle day. Doppler evaluation was done on the day of embryo transfer.
Women recruited in the study were scanned transvaginally with colour blood flow imaging ~1 h before embryo transfer. Doppler sonographic measurements were carried out using a Doppler US (Acumen XP128/10; Acuson, Mountain View, CA, USA) machine equipped with a transvaginal transducer of 7 MHz. All scans were done by one operator (T.P.W.L.) experienced in the procedure. The women were studied between 0800 and 0900 h to exclude the effects of circadian rhythmicity on blood flow (Zaidi et al., 1995). 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 it entered the uterus. Ovarian flow signals were obtained from within the ovarian parenchyma. The ovarian vessels studied were those detected in close proximity to the follicles. The `gate' of the Doppler was positioned when the vessel with good colour signals was identified on the screen. A visual classification was made using three similar, consecutive waveforms of good quality on the right and the left side; median values (range) were used. The pulsatility index (PI) and resistance index (RI) of the uterine and ovarian arteries were calculated electronically. As no significant differences in the Doppler velocimetry indices between the left and right side of the uterine and intra-ovarian arteries were obtained, the data were combined and the average value of both arteries was used. Furthermore, endometrial perfusion was also assessed by colour Doppler flow imaging. The presence or absence of colour and the number of colour signals obtained from the pulsatile vessels in the endometrium, which represented the spiral arteries, was then recorded. Women demonstrating
2 colour signals were considered to have absent or minimal flow. The velocity scale was set to detect low flow signals in the range of 00.23 m/s, while the colour gain was adjusted to minimize motion artifacts. The region of interest in the colour Doppler examination was adjusted to a minimum area with inclusion of the whole endometrium in mid-sagittal plane. The image was frozen on the screen and the number of pulsatile dots (representing spiral arteries) were counted at the upper two-thirds of the endometrium. However, the PI and RI of the spiral arteries were not recorded because the marked tortuosity of arteries made optimal placement of the `gain' difficult.
Statistical analysis
Statistical analysis was performed using Statistical Package for Social Science (SPSS for Windows package release 10.0; SPSS Inc., Chicago, IL, USA). The non-parametric MannWhitney U-test was used in the evaluation of the skewed data. As the data were not normally distributed, continuous data are expressed as median and range. A P value of < 0.05 was considered significant. The 2 test or the Fisher's exact test was used to estimate the significance of difference between discontinuous variables.
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Results |
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Discussion |
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Tekay et al. (1995) found no difference in mean uterine artery PI between asymptomatic and ovarian hyperstimulation cycles (Tekay et al., 1995). However, serum oestradiol concentrations in patients of ovarian hyperstimulation syndrome in Tekay's study population were similar to those in asymptomatic controls. Moreover, the Doppler evaluation was done in the late luteal phase of the cycle, and this may explain the difference from our results.
Perhaps an important observation from this study is the increase in the number of subjects demonstrating absent or minimal endometrial colour signals at high concentrations of oestradiol. As a possible explanation of these findings we further investigated oestradiol induced endometrial haemodynamic changes. The endometrial haemodynamic analysis of women who developed an excessive response (group B) revealed that 75% were associated with absent or poor endometrial colour signals. Additionally, significantly fewer numbers of signals were observed in this group of women compared with moderate responders. There appears to be a trend towards inadequate endometrial flow at very high oestradiol concentrations. If indeed there was absence or inadequate endometrial perfusion while blood flow in the uterine arteries increased it would suggest that the blood flow was shunted away from the uterine endometrium. The low PI and RI of the ovarian arteries indicate neovascularization and increased capillary permeability in the ovarian tissue of high responders. Therefore, the blood flow might be directed through the uteroovarian collaterals to the ovaries. Moreover, the increase in hormonal concentrations in the peripheral plasma leads to a decrease in peripheral vascular resistance (Goswamy et al., 1988; Goswamy and Steptoe, 1988
; Long et al., 1989
) and a decreased contractility of the uterine muscles. This results in relaxation and opening up of the small uterine vascular channels which may also cause an increase in the capillary permeability. In a recent study (Basir et al., 2001
) on the endometrial morphological changes at high concentrations of oestradiol a significantly greater number of vessels and endometrial oedema in women who responded excessively to ovarian stimulation was demonstrated. Therefore, it was postulated that the blood flow through these minute endometrial vessels may be very slow and the weak Doppler flow signals arising from them could not be picked up by the colour Doppler despite low uterine PI and RI. The increase in capillary permeability and dilatation leads to extravasation of fluid from the intercellular to extracellular compartments and hence endometrial oedema. In another study (Gannon et al., 1997
) the investigators suggested that the blood flow per capillary might actually be reduced during oedema. Successful implantation and continuing development of implanted embryo depends on a complex series of cellular and molecular events (Finn, 1977
; Cross et al., 1994
) between the blastocyst and the endometrium. The decline in blood flow could therefore impede the exchange of essential nutrients, bioactive molecules and reactive compounds that are vital for implantation. Zaidi et al. (1996) concluded that absent endometrial and intra-endometrial vascularization appeared to be a useful predictor of failure of implantation in IVF cycles (Zaidi et al., 1996
).
In this study our sample size was small and the spiral artery blood flow indices were not measured. Further larger prospective studies are required to confirm the effect of excessively high concentrations of serum oestradiol on endometrial blood flow. Power Doppler has a three-fold greater sensitivity to flow than colour Doppler, and is particularly useful for minute vessels with low-velocity flow (Schilds et al., 2000). This can serve to determine the haemodynamic environment of the endometrium under the influence of very high oestradiol. In addition to the utero-ovarian blood flow indices, subjective observation of spiral arteries may be a useful starting point to convert a semi-quantitative assessment into a quantitative value at least until more sophisticated techniques are available for routine monitoring of infertile women undergoing IVF. Present data provide substantial evidence to suggest that the circulatory adequacy of the endometrium, which is vital for embryo implantation, is compromised in high responders. Excessive concentrations of oestradiol may result in suboptimal blood flow to the endometrium. Therefore, very low uterine PI and RI may not be associated with better endometrial perfusion. The altered endometrial perfusion in high responders may contribute to a decline in endometrial receptivity. This may explain and substantiate our clinical data, which showed markedly diminished implantation and pregnancy rates in high responders in our IVF programme.
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Acknowledgements |
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Notes |
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References |
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Submitted on January 3, 2001; accepted on July 5, 2001.