Is large for gestational age in singletons born after frozen embryo transfer associated with freezing technique or endometrial preparation protocol? A longitudinal national French study.

This article investigates whether the increased risk of large for gestational age (LGA) observed in babies born after frozen embryo transfer (FET) is related to the embryo freezing technique or the endometrial preparation protocol. Analyzing data from 35 French assisted reproductive technology (ART) centers between 2014 and 2018, the study found that artificial endometrial preparation cycles are associated with a significantly higher risk of LGA compared to ovulatory cycles, while no difference in LGA risk was observed between the two freezing methods—vitrification and slow freezing—or between embryo developmental stages at freezing. The findings suggest that endometrial preparation protocols have a greater impact on fetal growth outcomes after FET than the freezing technique, with ovulatory cycles potentially minimizing the risk of fetal growth disorders.