Does the endometrial thickness on the day of the trigger affect the pregnancy outcomes after fresh cleaved embryo transfer in the clomiphene citrate-based minimal stimulation cycle?

Purpose Thin endometrium is often observed after clomiphene citrate (CC) administration for follicular development and is one of the reasons for embryo transfer (ET) cancelation or implantation failure. We retrospectively analyzed whether the endometrial thickness (EMT) on the days of the maturation trigger and ET are predictive factors of pregnancy outcomes after fresh cleaved ET in a CC-based minimal stimulation cycle (CC-cycle). Methods A total of 746 CC-cycles in vitro fertilization (IVF), followed by fresh cleaved ET, from November 2018 to March 2019 were analyzed. Associations between the pregnancy outcomes and EMT on the days of the trigger and ET were statistically evaluated. Results Although the EMT on the day of ET was not significantly associated with the ongoing pregnancy rate (adjusted odds ratio [AOR], 1.043; P = .3251), a decreased EMT on the day of the trigger was significantly associated with a low ongoing pregnancy rate (AOR, 1.154; P = .0042). Furthermore, the clinical pregnancy rate was significantly lower when the EMT was <7 mm on the day of the trigger during the CC-cycle. Conclusions These results suggest that measurement of the EMT on the day of the trigger could be effective for predicting the pregnancy outcomes after fresh cleaved ET during the CC-cycle.