[Medical and ethical basis for embryo cryopreservation]

As part of Assisted Reproductive Technologies (ART), the advent of embryo freezing lowered the number of embryos transferred, decreasing multiple births without jeopardizing pregnancy rates. Using vitrification technology, 90% of embryos survive after thawing, producing clinical pregnancy rates similar to those of fresh embryos (41.6%y 44.3% respectively). Furthermore, cumulative pregnancy rates, obtained after transferring fresh plus frozen/thawed embryos, can reach 70%. Frozen embryo transfers (FET) are reported by six of seven institutions, which are part of the Chilean ART registry, and altogether constitute 22.8% of all ART procedures. Increasing use of cryopreservation lowered overall multiple gestations from 33% in 1995 to 23% in 2011, reducing pre term births and perinatal mortality. For many people, embryo freezing generates ethical dilemmas, due to the potential risks to which embryos are exposed, and the uncontrolled accumulation and disposal of human embryos. Scientific evidence today shows that frozen/thawed embryos are not exposed to disproportionate risks, and by hindering its use, both women and their children are exposed to the risks of multiple gestation, repeated cycles of ovarian hormonal stimulation or the impossibility to afford repeated ART cycles. In this article, we provide biomedical, as well as ethical, arguments to sustain that embryo cryopreservation is not only justified but fundamental when offering infertility treatment with ART.