Atosiban may have no beneficial effect on embryo transfer outcomes in women without uterine abnormalities: a propensity score matching study

Atosiban decreases uterine contractions and thus possibly promote uterine receptivity in patients undergoing embryo transfer (ET). However, its effect on women with normal uterine cavities remains elusive. We aim to investigate how atosiban impacts pregnancy outcomes in autologous FET cycles from women without uterine abnormalities. A retrospective cohort study using propensity score matching (PSM). We collected data from all FET cycles conducted at Taipei Fertility Center (Taipei, Taiwan) between March 2020 and April 2023, under approval from the Institutional Review Board (No. A202205161). Women who were infertile due to non-uterine causes (male factor, tubal abnormalities, ovulation disorders, or unexplained infertility) were included in the study. Exclusion criteria were any persistent uterine abnormalities, severe endometriosis, repeated implantation failure, and known paternal or maternal genetic or autoimmune diseases. Participants were assigned to two groups, with or without atosiban administration prior to FET. Age, body mass index (BMI), type of endometrial preparation, type of embryos transferred (blastocyst or cleavage), ploidy status, and embryo quality were used as covariates for matching (1:1 ratio). Subgroup analysis with and without PSM on cycles with only euploidy embryo transferred was also evaluated to further clarify atosiban impact on FET outcomes. Among 1770 cycles initially enrolled in this study, 537 (30.3%) FET were performed with an intravenous dose of atosiban on the transfer day. After matching, 517:517 cycles from each group were included in the final analysis (n=1034). Implantation rate (IR) in cycles with atosiban did not surpass the control group both before (32.2% versus 33.6%, p>0.05) and after PSM (29.2% versus 28.8%, p>0.05). In the matched population, there was no improvement in clinical pregnancy rate (CPR) (48.2% versus 51.2%) and ongoing pregnancy rate (OPR) (39.2% versus 39.9%) (p>0.05). Early miscarriage rate (EMR) was slightly lower in women with atosiban (19.1% vs 24.1%, p= 0.12), but the difference became minor after PSM (19.5% vs 22.7%, p=0.38). In a subgroup analysis on women undergoing single euploidy embryo FET, no significant differences in IR, CPR (59.2% vs 63.9%), EMR (13.5% vs 10.3%) and OPR (50.8% vs 56.5%) were found between women with and without atosiban administration (p>0.05). Furthermore, PSM analysis for this subgroup population demonstrated that the pregnancy outcomes in women with single euploidy FET remained unimproved with the use of atosiban after being adjusted for type of cycle, maternal age and embryo quality (p>0.05). Atosiban has not demonstrated any advantageous impact on FET cycles among infertile women without uterine disorders. Therefore, the administration of atosiban in FET cycles should be selective and warrant further extensive investigation through large-scale and well-designed studies.