Perinatal outcomes in children born after fresh or frozen embryo transfer: a Catalan cohort study based on 14,262 newborns.

OBJECTIVE: To ascertain whether perinatal outcomes are affected by vitrification and/or controlled ovarian hyperstimulation (COH).

DESIGN: Register-based cohort study.

SETTING: Not applicable.

PATIENT(S): Women undergoing in vitro fertilization (IVF) between 2008 and 2012 using autologous or donated eggs who had a singleton pregnancy delivered from the 24th week onward.

INTERVENTION(S): Fresh embryo transfer (ET) or frozen-thawed ET in women undergoing IVF.

MAIN OUTCOME MEASURE(S): Primary outcome birthweight, and secondary outcomes gestational age at delivery, small for gestational age, mode of delivery, and perinatal mortality.

RESULT(S): In the autologous egg population, newborns from the fresh ET group had lower birthweight than the frozen-thawed ET group (3,152.9 ± 545.5g and 3,343.2 ± 532.3g, respectively), and this difference persisted even after adjusting for confounding factors, and the newborns had a higher risk of being small for gestational age (SGA). In contrast, among egg-donor recipients undergoing ET, the mean birthweight did not differ between the groups (3,165 ± 604.15 g and 3,143.60 ± 604.21g in the fresh and frozen-thawed ET groups, respectively); however, in the adjusted regression model birthweight was statistically significantly higher in the fresh ET group than the frozen-thawed ET group. The risk of SGA remained comparable between the fresh versus frozen-thawed ET groups. We observed no statistically significant differences in perinatal mortality between groups either in the autologous egg population or in the donor recipient group.

CONCLUSION(S): Perinatal outcomes are negatively affected by COH and not affected by the vitrification process.