Cryopreservation of embryos is the process of preserving an embryo at sub-zero temperatures, generally at an embryo-genesis stage corresponding to pre-implantation, that is, from fertilization to the blastocyst stage. In 1992, Tina Gibson was nearly 2 years old when a couple donated embryos that were frozen in a clinic in the Midwest. In February 2020, one of those embryos was implanted in Ms. Gibson, an elementary schoolteacher in Tennessee, and in October, she gave birth to a 6-pound, 13-ounce baby. Ms. Gibson and her husband, Ben, named her Molly. The birth broke the record for the longest-frozen embryo to result in a live birth. That record, according to the National Embryo Donation Center in Tennessee, was set in 2017, when Molly’s older sister, Emma, was born after an embryo from the same donor couple was implanted in Ms. Gibson.The birth is an exciting development that will allow fertility doctors to reassure prospective parents that an embryo frozen for years, ...