Uterine peristalsis exerts control over fluid migration after mock embryo transfer.

STUDY QUESTION What is the effect of uterine peristalsis on fluid migration after mock embryo transfer? SUMMARY ANSWER Uterine peristaltic wave frequency was positively correlated with the distance that fluid moved after it was deposited in the uterine cavity. WHAT IS KNOWN ALREADY Embryos have been found outside the uterine cavity after embryo transfer. It has been suggested that uterine contractions expelled these embryos. STUDY DESIGN, SIZE, DURATION A prospective cohort study of a total of 112 infertile women was conducted between March 2013 and May 2013. PARTICIPANTS/MATERIALS, SETTING, METHODS Uterine peristaltic activity was assessed before and after a mock embryo transfer, in which 20 µl of ultrasound contrast agent was placed in the uterine lumen 3 days after ovulation in a natural cycle. The movement of this fluid was measured by ultrasound at 0, 15 and 30 min after placement. MAIN RESULTS AND THE ROLE OF CHANCE The uterine peristaltic wave frequency was significantly higher after than before mock transfer (3.06 ± 0.99 versus 2.24 ± 0.74, P < 0.01). At the conclusion of the 30-min monitoring period, the fluid had remained in place (N = 94), leaked into the cervix (N = 5), or moved into the Fallopian tubes or the cornua of the uterus (N = 11). The fluid movement was positively correlated with uterine peristaltic wave frequencies before (r = 0.518, P < 0.01) and after embryo transfer (r = 0.371, P < 0.01) and uterine peristaltic wave frequency was significantly higher both before and after embryo transfer in cases where the fluid was extruded. LIMITATIONS, REASONS FOR CAUTION Mock embryo transfer was performed in the luteal phase of a natural cycle instead of a controlled ovarian stimulation cycle. The endometrial environment and uterine peristalsis may be different in a stimulated cycle. WIDER IMPLICATIONS OF THE FINDINGS Uterine peristalsis exerts control over embryo migration and could adversely affect the chances of pregnancy if the wave frequency is too high. It could be used as a predictor of uterine irritability before embryo transfer. STUDY FUNDING/COMPETING INTEREST(S) The authors declare that they have not received any particular study funding and do not have competing interests in this study.