Vitrification of human hatched blastocysts: a report of 4 cases

BACKGROUND: Vitrification is a fairly well-established technique for cryopreservation of human zona-intact blastocysts. However, little is known about the efficacy of the vitrification technique for zona-free hatched blastocysts. CASE: A total of 4 hatched blastocysts from 4 healthy, infertile women undergoing in vitro fertilization were vitrified and warmed. All 4 hatched blastocysts expanded after warming and were transferred to 4 patients. Three of the women became clinically pregnant. Two healthy infants were born in 2 deliveries, and 1 pregnancy had progressed to 35 weeks at this writing. CONCLUSION: Our results suggest that vitrification is a useful cryopreservation technique not only for zona-intact blastocysts but also for zona-free hatched blastocysts.