Letrozole-induced endometrial preparation improved the pregnancy outcomes after frozen blastocyst transfer compared to the natural cycle: a retrospective cohort study

Abstract

Background Letrozole treatment is considered an effective option in endometrial preparation for frozen embryo transfers in patients with ovulation disorders or irregular menstruation; however, the effectiveness of letrozole-induced endometrial preparation remains unclear in ovulatory patients. Furthermore, there is no comparative study reporting on pregnancy complications and congenital anomalies after frozen embryo transfers comparing natural and letrozole-assisted cycles. This study examined whether letrozole-induced endometrial preparation affected pregnancy outcomes, perinatal outcomes, and congenital anomalies after single vitrified-warmed blastocyst transfers (SVBTs) in ovulatory patients, as compared with the natural cycle. Methods This historic cohort study included only patients with unexplained infertility. Overall, 14,611 patients who underwent SVBTs between July 2015 and June 2020, comprising both natural and letrozole-assisted cycles, were included. Multiple covariates that impact outcomes were used for propensity score matching; 1,911 patients in the letrozole group were matched to 12,700 patients in the natural group, and the clinical records of 1,910 patients in each group were retrospectively analysed. Cycle characteristics, pregnancy outcomes (clinical pregnancy, ongoing pregnancy, and live birth), and incidence of pregnancy complications and congenital anomalies were statistically compared between the two groups. Results Multivariate logistic regression analysis showed that letrozole administration during SVBT cycles significantly improved the live birth rate (P = 0.0355). Gestational age, birth length, birth weight, and infant sex, as well as the incidence of pregnancy complications and birth defects, were statistically comparable between the two groups. Furthermore, multivariate logistic regression analysis revealed that the perinatal outcomes were not affected by letrozole-induced endometrial preparation. Conclusions Letrozole-induced endometrial preparation improved the live birth rate compared with the natural cycle, without adverse effects on perinatal outcomes and congenital anomalies after SVBTs. Therefore, letrozole-induced endometrial preparation might be a safe and more effective strategy, especially for patients with insufficient luteal function.

The definition of unexplained infertility: A systematic review

“…Of the remaining 375 papers, 117 did not classify a definition of unexplained infertility. As a result, a total of 258 primary research papers with full text available were included …”

Fatty acid supplementation during warming improves pregnancy outcomes after frozen blastocyst transfers: a propensity score-matched study

“…From June 2023 to August 2023, we warmed them using FA‐supplemented solutions (VT526; Kitazato Corporation), representing the FA group. We performed propensity score matching using JMP software (SAS, Cary, NC, USA) to reduce bias in patient characteristics 50 , 51 . Briefly, we used multiple covariates, including previous oocyte retrieval cycles, embryo transfers, and endometrial thickness on the day of SVBT, for propensity score matching.…”

“…SVBTs were performed under vaginal ultrasound guidance using a specially designed soft silicone inner catheter (Kitazato ET catheter; Kitazato Corporation). A single embryo was placed in a minimal volume in the upper part of the uterine cavity 51 . Dydrogesterone (Duphaston, 30 mg/day; Mylan EPD G.K., Tokyo, Japan) was administered orally during the early luteal phase after SVBT.…”

Fatty acid supplementation into warming solutions improves pregnancy outcomes after single vitrified‐warmed cleavage stage embryo transfers

“…Early pregnancy loss and miscarriage during the first trimester were defined according to the absence of a gestational sac after implantation and the absence of a fetal heartbeat after the confirmation of a gestational sac. 32 …”

“…The clinical and ongoing pregnancy rates were defined according to the ultrasonographic observation of a gestational sac at 3 weeks after SVCT, and the observation of a fetal heartbeat was performed 5 weeks after SVCT. Early pregnancy loss and miscarriage during the first trimester were defined according to the absence of a gestational sac after implantation and the absence of a fetal heartbeat after the confirmation of a gestational sac 32 …”