Abnormal Endometrial Peristalsis in Frozen-Thawed Embryo Transfer: Risk Factors and Improvements of Atosiban Treatment

This retrospective study investigated factors associated with abnormal endometrial peristaltic waves (EPWs) and evaluated the impact of Atosiban intervention on clinical outcomes in frozen-thawed embryo transfer (FET) cycles. A total of 7554 infertile women undergoing FET cycles were assessed using one-minute transvaginal ultrasound examinations one day before transfer to determine peristaltic frequency and direction. Logistic regression identified maternal reproductive history and cycle characteristics as parameters associated with abnormal EPWs. Among women with abnormal EPWs (n=515), Atosiban was administered before embryo transfer, while controls (n=7039) did not. After propensity score matching (approximately 1:2), 505 treated cycles were compared with 993 control cycles. Overall, pregnancy outcomes were comparable between groups, although Atosiban administration was associated with a modest improvement in clinical pregnancy rate (CPR) (58.6 % vs. 53.3 %; P=0.049). Subgroup analysis by embryo stage revealed that this benefit was mainly observed in cleavage-stage (Day 3) embryo transfers (50.2% vs. 41.4%; P=0.025), with no significant effect in blastocyst (Day 5/6) transfers. These findings suggest that abnormal EPWs are influenced by multiple clinical factors, and Atosiban intervention may improve pregnancy outcomes, particularly in cleavage-stage embryo transfer cycles. Lay Summary A successful pregnancy after frozen embryo transfer cycles depends on proper coordination between the embryo and the uterus. In some cases, the uterus shows abnormal movements - called abnormal endometrial peristaltic waves (EPWs) - which may make it harder for implantation. In this study, we analyzed medical data from over 7,500 women who had frozen embryo transfers. About 500 of them showed abnormal EPWs during an ultrasound check before the embryo transfer. These women received a medication (Atosiban) which helps relax the uterus. We found that abnormal uterine movements can be caused by several factors. After receiving treatment, women with abnormal movements had better pregnancy chances, similar to those without the problem. The benefit was even greater when embryos were transferred at an early stage (Day 3 embryos). This suggests that detecting and treating abnormal uterine movements could improve the chances of pregnancy for some women undergoing IVF, especially those receiving early-stage embryos.