Department of Obstetrics and Gynecology, Stanford School of Medicine, 300 Pasteur Drive, HH333, Stanford, CA 94305, USA
1 To whom correspondence should be addressed. e-mail: milki4{at}aol.com
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Abstract |
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Key words: embryo transfer/IVF/ultrasound uterine position
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Introduction |
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The purpose of our study was to determine the consistency of uterine position at actual embryo transfer as compared with mock embryo transfer, depending on whether the uterus is initially anteverted (AV) or retroverted (RV), in a large series of IVF patients.
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Materials and methods |
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Statistical analysis was performed using 2-test and Students t-test, when appropriate. Statistical significance was set at P < 0.05.
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Results |
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For patients undergoing a frozenthawed embryo transfer, 114 cycles were in patients identified to have an AV uterus at mock embryo transfer. In these cycles, 100 (88%) remained AV and 14 (12%) became RV. By comparison, in 46 cycles performed in patients with an RV uterus, 31 (67%) remained RV and 15 (33%) became AV. Again, compared with patients with AV uterus at mock embryo transfer, those with an RV uterus were significantly more likely to change position (P = 0.01) at thawed embryo transfer, although the difference was not as striking as for fresh embryo transfer.
For patients with an AV uterus at mock embryo transfer, significantly more changed to RV at the time of thawed embryo transfer (14/114) compared with fresh embryo transfer (15/623; P = 0.001). Conversely, for patients with an RV uterus at mock embryo transfer, more changed position at the time of fresh embryo transfer (118/213) than at the time of thawed embryo transfer (15/46; P = 0.01).
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Discussion |
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In our program, we have routinely conducted mock embryo transfer at a date prior to the actual embryo transfer. For the last several years, the mock embryo transfer and the actual embryo transfer have been both performed under transabdominal ultrasound guidance. This practice has provided us the opportunity to assess the uterine position at each of these procedures. Our data suggest that when the uterus is AV at mock embryo transfer, it is very likely to remain so at the time of actual fresh embryo transfer (98%). Slightly more than one-quarter of our patients were found to have an RV uterus at mock embryo transfer. This rate is similar to that previously reported in the literature for the general gynaecology population (Kivijarvi and Gronroos, 1983; Chi et al., 1990
; Thompson, 1997
). In these patients, there was a significant chance that the uterus would become AV at the time of actual embryo transfer (55%) in fresh IVF cycles. For thawed embryo transfer cycles, the same pattern was noted, where significantly more RV uteri became AV compared with the reverse. The difference, although statistically significant, was not as pronounced. This is consistent with the expectation that the enlarged ovaries lying in the posterior cul-de-sac are a factor in fresh embryo transfer cycles, where controlled ovarian hyperstimulation (COH) is used, and not a factor in thawed embryo transfer, when the cycle is natural.
In view of the enlarged ovaries resulting from COH, it is expected that more AV uteri would remain AV at the time of fresh embryo transfer (98%) compared with thawed embryo transfer (88%) performed in a natural cycle. For patients with an RV uterus at mock embryo transfer, more converted to AV at fresh embryo transfer (55%) than at thawed embryo transfer (33%). In this group, there was a significantly higher number of oocytes recovered in fresh cycles when the uterus changed from RV to AV (11.0 ± 6.4) compared with when the uterus remained RV (8.8 ± 5.8) (P = 0.01), again confirming the role of the ovarian size in changing the uterine position. However, the fact that the conversion of the uterus from RV to AV was still seen in one-third of the thaw cycles suggests that the ovarian volume is not the only factor that may play a role in uterine position change.
Both the mock and real embryo transfers were performed under transabdominal ultrasound guidance, with a full bladder for adequate ultrasound visualization. We were, however, more likely to require a fuller bladder for the real embryo transfer, where, in addition to visualization, more complete straightening of the cervico-uterine angle is desirable (Sundstrom et al., 1984; Lewin et al., 1997
). The impact of bladder fullness weighing down on the uterus is more likely to prevent anteversion of the uterine position. Therefore, the effect of the full bladder, if anything, would have decreased the conversion from RV to AV at the time of embryo transfer.
Although transabdominal ultrasound-guided embryo transfer is used by many IVF programs, it is far from being a universal practice. Many physicians feel comfortable that the clinical touch can lead to an adequate placement of the embryos in the uterine cavity. It can be argued that experienced IVF practitioners can feel their way along the cervical and endometrial canal while threading the embryo transfer catheter, and thus, it may not be critical for them to visualize the uterine position during embryo transfer. If this is the case, the findings of our study, which show a change in the position of an RV uterus more than half the time, may not carry much relevance. However, based only on clinical touch, many clinicians may be unaware that malpositioning of the catheter is occurring (Strickler et al., 1985; Woolcott and Stanger, 1997
; Kan et al., 1999
). A gentle direction of the catheter following the contour of the endometrial cavity is essential to avoid disrupting the endometrium and eliciting deleterious uterine contractions, which may expel an embryo. (Fanchin et al., 1998
; Lesny et al., 1998
). An accurate knowledge of the uterine angle at the time of embryo transfer will help with a smooth single motion passage of the embryo transfer catheter. Assuming that an RV uterus at mock embryo transfer will remain RV at actual embryo transfer may initially mislead the practitioner performing the procedure. The realization of a change in uterine position may come only after some hesitation and subtle trauma to the uterus or risk of plugging the catheter tip with endometrium (Nabi et al., 1997
; Kan et al., 1999
). This hesitation may lead to the unnecessary application of a tenaculum to straighten the uterine angle, which may also induce harmful uterine contractions (Lewin et al., 1997
; Lesny et al., 1999
). The orientation of the cervix in the vaginal vault may provide an indication of the uterine position in many instances; however, this may not always be accurate.
Ultrasonographic guidance during embryo transfer offers the benefits of catheter visualization to confirm passage beyond the internal os and avoid touching the uterine fundus (Woolcott and Stanger, 1997; Wood et al., 2000
; Schoolcraft et al., 2001
). In addition, the lack of consistency between uterine position at mock and actual embryo transfer for patients with RV uteri further supports the use of transabdominal ultrasound guidance in order to more accurately assess the cervico-uterine angle at the time of embryo transfer and gently guide the catheter into the endometrial cavity.
From a practical standpoint, even for programs that routinely practice transabdominal ultrasound-guided embryo transfer, knowing that an RV uterus will more often than not become AV at embryo transfer supports asking all patients to present for embryo transfer with a full bladder. It has been our experience that patients with a known RV uterus are often instructed to have an empty bladder, or possibly a minimally full bladder, to provide a sonic window for ultrasound visualization, during embryo transfer. For those whose uterus is pushed to an AV position by the enlarged ovaries in the posterior cul-de-sac, a substantially fuller bladder is desirable for a smooth transfer. Presenting with an empty bladder may lead to a suboptimal transfer or entail a significant delay in performing the embryo transfer at the scheduled time. Even for patients with an RV uterus undergoing a frozenthawed embryo transfer, the recommendation for a full bladder is likely to be beneficial, since one-third of these will convert to an AV position.
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References |
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Submitted on July 22, 2003; accepted on November 10, 2003.
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