The Effect of Uterine Contractions on Fertility Outcomes in Frozen Embryo Transfer Cycles: A Cohort Study

BACKGROUND: The relationship between uterine peristalsis before embryo transfer and the success of assisted reproductive techniques (ARTs) has not been properly investigated. In this study, the effect of uterine contractions on embryo implantation in frozen embryo transfer (FET) cycles was investigated to determine whether the frequency of uterine contractions can be used as a quantitative marker to assess endometrial receptivity. METHODS: In this cohort study of 68 eligible FET candidates, one hour before embryo transfer (ET), frequency of uterine contractions was assessed with transvaginal ultrasonography. Patients were followed up for 20 weeks. The association between FET outcomes including clinical pregnancy, abortion, and ectopic pregnancy with uterine contractions was evaluated. Binary logistic regression was conducted to test the association between clinical pregnancy outcomes in different groups. The p<0.05 were considered statistically significant. RESULTS: Of 68 patients, 25 (36.8%) experienced clinical pregnancy. Multiple logistic regression for omitted confounders (age, BMI, duration, type and cause of infertility) revealed that patients with uterine peristaltic wave frequency less than 2≤ wave/min had higher chance of successful pregnancy compared to those with ≥4 wave/min (odds ratio: 10.8; 95% confidence interval: 1.5–79.4, p=0.019). The Pearson's correlation showed a statistically significant relationship between the frequency of uterine contraction and endometrial thickness (r= 0.42, p=0.002). CONCLUSION: Patients with uterine peristalsis of <4.0 wave/min before embryo transfer had a higher chance of successful implantation and pregnancy compared with those with higher contraction frequencies. It seems that measuring uterine contraction frequency before embryo transfer might help to predict pregnancy outcomes.