Assisted reproductive technology
Follicular development was stimulated with the long protocol as described previously [Oocytes were collected transvaginally 36 h after hCG administration and inseminated as described previously [Redundant embryos were cultured for 5 to 6 days after IVF/ICSI to the blastocyst stage and cryopreserved using a vitrification method. Thawed cryopreserved blastocysts were transferred to uteri on luteal day 5 of a spontaneous natural cycle, as described previously [