Background & Objective: To study whether children born after vitrified–thawed embryo transfers (ETs) using donated oocytes have worse perinatal outcomes when compared with fresh ET. Methods: Patients with a first singleton live birth after single blastocyst transfer were compared using multivariable regression analysis to account for potential confounding factors. The primary outcome was birth weight. Secondary outcomes were birth weight z-scores and percentiles, small/large for gestational age, gestational age at delivery, gender, prematurity (<37 weeks and <32 weeks), neonatal morbidity (Apgar scores and need for neonatal intensive care) and maternal morbidity (gestational hypertensive disorders, gestational diabetes and caesarean delivery). Results: There was no significant difference between the fresh ET and FET groups in terms of mean birth weight and birth weight z-scores, in both the unadjusted and confounder-adjusted models. However, artificial endometrial preparation was associated with a higher birth weight and birth weight z-scores when compared with a transfer in a natural cycle. Although a 1-day statistically significant difference in gestational age at birth was detected, premature birth rates (<37 weeks) did not vary significantly between groups. No other statistically significant differences were found in the remaining neonatal and maternal outcomes studies between the fresh ET and FET groups. Conclusion: No significant difference in birth weight and prematurity rates between fresh or frozen embryo transfers (FETs) in new-borns after oocyte donation was found.

Background & Objective: To study whether children born after vitrified–thawed embryo transfers (ETs) using donated oocytes have worse perinatal outcomes when compared with fresh ET. Methods: Patients with a first singleton live birth after single blastocyst transfer were compared using multivariable regression analysis to account for potential confounding factors. The primary outcome was birth weight. Secondary outcomes were birth weight z-scores and percentiles, small/large for gestational age, gestational age at delivery, gender, prematurity (<37 weeks and <32 weeks), neonatal morbidity (Apgar scores and need for neonatal intensive care) and maternal morbidity (gestational hypertensive disorders, gestational diabetes and caesarean delivery). Results: There was no significant difference between the fresh ET and FET groups in terms of mean birth weight and birth weight z-scores, in both the unadjusted and confounder-adjusted models. However, artificial endometrial preparation was associated with a higher birth weight and birth weight z-scores when compared with a transfer in a natural cycle. Although a 1-day statistically significant difference in gestational age at birth was detected, premature birth rates (<37 weeks) did not vary significantly between groups. No other statistically significant differences were found in the remaining neonatal and maternal outcomes studies between the fresh ET and FET groups. Conclusion: No significant difference in birth weight and prematurity rates between fresh or frozen embryo transfers (FETs) in new-borns after oocyte donation was found.