Uterine position at real embryo transfer compared with mock embryo transfer

M.B. Henne and A.A. Milki1

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


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
BACKGROUND: The purpose of this study was to determine the consistency in the uterine position between mock and real embryo transfer. METHODS: We reviewed 996 consecutive embryo transfer cycles (585 patients); 74% of patients had an anteverted (AV) uterus and 26% had a retroverted (RV) uterus at mock embryo transfer. All mock and real embryo transfers were performed under abdominal ultrasound guidance. RESULTS: Of 623 fresh embryo transfers in patients with an AV uterus at mock embryo transfer, only 2% became RV, while 55% of 213 embryo transfers in patients with an RV uterus on mock embryo transfer converted to AV at real embryo transfer (P < 0.0001). For frozen–thawed embryo transfer, 12% of AV uteri at mock embryo transfer became RV, while 33% of RV uteri became AV (P = 0.01). CONCLUSIONS: Our data suggest that an RV uterus at mock embryo transfer will often change position at real embryo transfer. Misdirecting the embryo transfer catheter can be avoided by accurate knowledge of the uterine position at the time of embryo transfer, which can be more accurately assessed by routine ultrasound guidance. Additionally, patients with an RV uterus at mock embryo transfer should still present with a full bladder for embryo transfer, since a significant number will convert to an AV position.

Key words: embryo transfer/IVF/ultrasound uterine position


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
During IVF treatment, the embryo transfer step is a critical final procedure (Mansour et al., 1990Go; Sharif et al., 1995Go; Hearns-Stokes et al., 2000Go; Schoolcraft et al., 2001Go; Mansour and Aboulghar, 2002Go). Although perceived as a simple non-surgical intervention, the smooth performance of embryo transfer significantly impacts the outcome of IVF. A trial or mock embryo transfer is commonly practiced to assess uterine depth and position, in preparation for an optimal real embryo transfer (Mansour et al., 1990Go; Knutzen et al., 1992Go; Sharif et al., 1995Go). The uterine position may vary between mock and real embryo transfer, possibly due to the enlarged stimulated ovaries. These larger ovaries could rest in the posterior cul-de-sac, pushing the uterus anteriorly, or they may lie above the uterus and push it posteriorly. We, like many IVF practitioners, have on multiple occasions observed a change in uterine position between mock and real embryo transfer (Strickler et al., 1985Go; Sharif et al., 1995Go). However, the actual incidence of such a change has not been systematically examined in the literature.

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.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
We reviewed the charts of all patients undergoing an embryo transfer by the senior author between January 1, 2001 and December 31, 2002. All IVF patients underwent transabdominal ultrasound-guided mock embryo transfer during the follicular phase of an unstimulated cycle, or while on oral contraceptive pills prior to treatment. Uterine position and endometrial cavity depth were documented. All real embryo transfers were conducted under transabdominal ultrasound guidance, and uterine position was noted. Embryos were placed 1–1.5 cm below the uterine fundus as previously measured at mock embryo transfer, guided and modified, if necessary, by ultrasound monitoring. Frozen–thawed embryo transfers were performed in unstimulated cycles using the findings of the original mock embryo transfer, prior to the fresh cycle, as the reference.

Statistical analysis was performed using {chi}2-test and Student’s t-test, when appropriate. Statistical significance was set at P < 0.05.


    Results
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Embryo transfer was performed in 996 cycles in 585 patients. An AV uterus was identified at mock embryo transfer in 434 patients (74%), while 151 patients (26%) were noted to have an RV uterus. Fresh and frozen–thawed embryo transfer cycles were analysed separately. The results are summarized in Table I.


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Table I. Uterine position at actual ET compared with mock ET
 
There were 623 fresh IVF-embryo transfer cycles in patients with an AV uterus at mock embryo transfer. Of these, 608 (98%) remained AV. In contrast, 213 fresh cycles were completed in patients with an RV uterus at mock embryo transfer, of which only 95 (45%) remained RV, while 118 (55%) converted to an AV position. Thus, patients with RV uterus at mock embryo transfer were significantly more likely to change position (P < 0.0001) at the time of actual embryo transfer.

For patients undergoing a frozen–thawed 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).


    Discussion
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
There is a consensus in the IVF community that a smooth embryo transfer is critical for achieving high success rates (Kovacs, 1999Go; Hearns-Stokes et al., 2000Go; Schoolcraft et al., 2001Go; Mansour and Aboulghar, 2002Go). To this end, a trial embryo transfer is commonly performed on patients at some point prior to the actual embryo transfer. Many practitioners advocate the use of transabdominal ultrasound guidance during embryo transfer (Leong et al., 1986Go; Hurley et al., 1991Go; Kan et al., 1999Go; Wood et al., 2000Go; Coroleu et al., 2000Go; 2002Go); however, this practice is not uniformly employed. In a survey by Kovacs (1999)Go about the relative importance of different factors affecting the success of embryo transfer, ultrasound guidance was ranked 11 out of 12 possible factors.

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, 1983Go; Chi et al., 1990Go; Thompson, 1997Go). 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., 1984Go; Lewin et al., 1997Go). 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., 1985Go; Woolcott and Stanger, 1997Go; Kan et al., 1999Go). 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., 1998Go; Lesny et al., 1998Go). 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., 1997Go; Kan et al., 1999Go). 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., 1997Go; Lesny et al., 1999Go). 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, 1997Go; Wood et al., 2000Go; Schoolcraft et al., 2001Go). 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 frozen–thawed 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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Submitted on July 22, 2003; accepted on November 10, 2003.





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