title: Cryopreservation of IVF embryos: which stage?
abstract: Embryo freezing is a mandatory tool in IVF technology as controlled ovarian hyperstimulation usually leads to extra embryos which are not transferred. One dilemma is the embryonic stage at which the embryos are to be frozen. Early stage freezing (PNs or cleavage stage) leads to a two step selection: at the time of thawing and a few hours or a day after. Then the recovering embryos are submitted to the classical in vitro developmental arrests in relation with maternal, paternal and cytogenetic factors. The "take home baby rate" per frozen embryo is low, rarely over 5%. Blastocyst have overcome the blocks in vitro: a first selection has already been made. The quality of freezing at this stage depends greatly on the culture conditions. It allows freezing of fewer embryos, but with higher yields: a >10% take home baby rate can be expected. It is clear to us that vitrification, beside the technical problems, has to be handled with care, especially if ethylene glycol (EG) is used. Metabolic products of EG might have negative effects on organogenesis.
authors.affiliation: Laboratoire Marcel Mérieux, Institute Rhonalpin, 1 Rue Laborde, 69500 Bron, France. ymenezo@lab-merieux.net
authors.forename: Y
authors.initials: Y
authors.lastname: Menezo
mesh_terms: D000818:Animals; D001755:Blastocyst; D015925:Cryopreservation / Q000379:methods*; D003451:Cryoprotective Agents; D004624:Embryo Transfer; D004622:Embryo, Mammalian; D005307:Fertilization in Vitro; D006801:Humans
chemical_list: D003451:Cryoprotective Agents