Comparison of the perinatal outcomes of live-born singletons between blastocysts and cleavage-stage embryo transfer in FET cycles via propensity score matching.

Background: In previous studies, the incidences of premature births and large for newborn gestational age (LGA ) infants were higher with blastocyst transfer than with cleavage-stage embryo transfer in infants conceived via frozen embryo transfer (FET) cycles. However, those previous studies reported unbalanced baseline characteristics between the blastocyst transfer group and the cleavage embryo transfer group. Therefore, in this study, we used propensity score matching to compare the birth weight and newborn gestational age of live-born singletons between blastocyst and cleavage-stage embryo transfer in FET cycles.

Methods: From January 2018 to April 2023, 706 cases of singleton delivery resulting from FET cycles that met the inclusion and exclusion criteria were included in this study, of which 180 cases resulted from cleavage embryo transfer and 526 cases resulted from blastocyst transfer. Using propensity score matching, we obtained a well-balanced cohort with 173 pairs of cases. We compared the neonatal perinatal outcomes of this cohort, including birth weight and newborn gestational age, which are the primary outcomes. Moreover, we used multivariate linear regression to analyze whether the type of embryo transferred in a FET cycle was correlated with neonatal birth weight or newborn gestational age.

Results: After propensity score matching, there were no significant differences in any of the baseline characteristics between the blastocyst transfer group and cleavage-stage embryo transfer group. There were also no differences between the two groups in terms of the mean birth weight (g) (3380 [3050,3665] vs. 3380 [3002.5,3650], p = 0.941), newborn gestational age (days) (275 [269,280] vs. 275 [270,281], p = 0.282) or other perinatal outcomes. Multiple linear regression analysis revealed that the type of embryo transferred in a FET cycle was not correlated with neonatal birth weight or gestational age.

Conclusions: Blastocyst transfer had perinatal outcomes similar to those of cleavage-stage embryo transfer for live-born singletons in FET cycles and did not influence the mean birth weight or gestational age of the neonates.

Clinical trial number: Not applicable.