Pregnancy and live birth following the transfer of vitrified-warmed blastocysts derived from zona- and corona-cell-free oocytes.

This study reports two clinical pregnancies and one live birth following the transfer of vitrified blastocysts developed from oocytes with neither zona pellucida nor corona cells. Two zona-free oocytes obtained from two patients of advanced maternal age undergoing minimal stimulation were normally fertilized after intracytoplasmic sperm injection. In case 1, all four blastomeres of the zona-free embryo were loosely associated and inserted back into ruptured zona on day 2. Zona-free embryo from case 2 had tight contacts between blastomeres and was cultured without zona. Both embryos derived from zona-free oocytes progressed to blastocyst stage and were cryopreserved by vitrification. When patients came back for a cryopreserved embryo transfer, both vitrified blastocysts survived warming. In case 1, transfer of a warmed blastocyst with reconstructed zona resulted in a clinical pregnancy that ended in a spontaneous abortion at 22 weeks. In case 2, live birth was achieved with a normal healthy baby (male) weighing 2381 g at 40 weeks' gestation. This report emphasizes the importance of maintenance of normal cell arrangement on the subsequent embryonic development for a zona-free oocyte. Zona-free oocytes may provide a valuable source of embryos for infertility patients, especially for those with a limited number of oocytes.