Fresh embryo transfer results in altered placental epigenetic regulation: a rationale for frozen embryo transfer

Because assisted reproductive technologies (ARTs) have become increasingly effective, much attention has shifted toward the safety and outcomes of children born from these techniques. For comparing the outcomes of different methodologies at each step in the ART process, 1 step noted to have a differential effect is the timing of embryo transfer (ET), whether it is a fresh ET or a frozen embryo transfer (FET). Indeed, several publications have reported differing rates of low birth weight, prematurity, abnormal placentation, and gestational hypertension or pre-eclampsia between these 2 ET modalities (1, 2).