Uterine peristalsis before embryo transfer affects the chance of clinical pregnancy in fresh and frozen-thawed embryo transfer cycles

Does uterine peristalsis influence the chance of clinical pregnancy in an embryo transfer cycle? The uterine peristaltic wave frequency before embryo transfer is inversely related to the clinical pregnancy rates in fresh and frozen-thawed embryo transfer cycles. Uterine peristalsis participates in regulating fluid migration after mock embryo transfer, but whether it could potentially influence pregnancy outcomes had remained unclear. This prospective cohort study included a total of 292 infertile women and was conducted between March 2013 and August 2013. Patients underwent fresh embryo transfer in a fresh stimulation cycle with a long down-regulation protocol, a natural frozen-thawed embryo transfer cycle or an artificial frozen-thawed embryo transfer cycle. Uterine peristaltic activity was assessed before embryo transfer by transvaginal ultrasonography. The uterine peristaltic wave frequencies of most patients were between 1.1 and 3.0 waves/min before embryo transfer (ET). The clinical pregnancy rate was the highest when < 2.0 waves/min was observed and it decreased with an increasing wave frequency thereafter, with an especially dramatic decrease with > 3.0 waves/min. Uterine peristaltic wave frequencies of the non-pregnant patient group were higher than that of the clinically-pregnant patient group in all types of transfer, fresh embryo transfer, natural FET or artificial FET cycle. Binary logistic regression analysis demonstrated that the association between uterine peristaltic wave frequency before embryo transfer and clinical pregnancy was independently significant (odds ratio: 0.49; 95% confidence interval: 0.34-0.70, P < 0.001). Uterine peristalsis after embryo transfer was not observed in case any possible negative effect of the observation disturbed embryo implantation or caused psychological stress. Uterine peristalsis after embryo transfer may differ from that before embryo transfer. Another limitation of the present study was the lack of uterine peristaltic wave type analysis which is also an important parameter to assess uterine activity. Patients with uterine peristalsis of < 3.0 waves/min before embryo transfer had a higher chance of pregnancy compared with those with higher frequencies. This could be a promising quantitative marker of uterine receptivity and pregnancy outcome in an embryo transfer cycle. The predictive validity of the cut-off value needs to be tested in further study.