Vitrification does not affect birth weight: lessons from the oocyte donation model.

Research Question: Is embryo cryopreservation a cause of high birth weight and large for gestational age (LGA) in singletons resulting from vitrified-warmed embryo transfer?

Design: Retrospective cohort study evaluating 670 oocyte recipients who underwent fresh (367 cycles) or vitrified-warmed embryo transfer (303 cycles) at Instituto Bernabeu between July 2017 and March 2019. All single blastocyst transfers carried out in an artificial cycle that resulted in a singleton live birth were included.

Results: Maternal age (42.

Early epigenetic reprogramming in fertilized, cloned, and parthenogenetic embryos.

Despite ongoing research in a number of species, the efficiency of embryo production by nuclear transfer remains low. Incomplete epigenetic reprogramming of the nucleus introduced in the recipient oocyte is one factor proposed to limit the success of this technique. Nonetheless, knowledge of reprogramming factors has increased-thanks to comparative studies on reprogramming of the paternal genome brought by sperm on fertilization-and will be reviewed here.