INTRODUCTION

Perinatal risks after frozen embro transfer (FET) have been reassuring but some authors suggest that birthweights are higher after FET than after fresh embryo transfer (ET). The primary objective of this retrospective study, conducted in Clinique de la Sagesse, Rennes (France) from December 2013 to March 2017, was to determine whether a difference in birthweight exists between children conceived through in vitro fertilization (IVF) with frozen versus fresh ET. The secondary objective was to compare live birth rates after frozen versus fresh cycles.

MATERIAL AND METHODS

All couples undergoing IVF were included. Cycles with gamete donation and twin pregnancies were excluded. Hormone therapy was used in all embryo transfers. The main outcome measures were the child's birthweight, mode of delivery, gestation length and sex, maternal characteristics, and IVF characteristics. The primary endpoint was birthweight.

RESULTS

We studied 5406 embryo transfers and the 708 resulting singleton live births on which birthweight data were available. Mean birthweight was 3357g after frozen embryo transfer versus 3183g after fresh embryo transfer (p<0.001). After adjusting for confounding factors, the children born after frozen embryo transfer were 165.2g heavier (95%CI [92.96-237.51]). No difference was found in gestation length. Live birth was obtained after the 1.6th IVF attempt. Live birth rate was higher for fresh cycles (19% versus 12%, p<0.001), and the caesarean rate lower (16% versus 21%).

DISCUSSION

Birthweight was higher after frozen embryo transfer for a similar gestational age. Further research is needed to elucidate the mechanisms responsible for this difference.