Successful dizygotic twin pregnancy after recryopreservation by vitrification of human expanded blastocysts developed from frozen cleaved embryos on day 6: a case report

BACKGROUND: Vitrification has evolved into an established technique for cryopreservation of human blastocysts. However, it is still unclear whether the blastocysts developed from frozen embryos can be cryopreserved a second time by vitrification for further embryo transfer. CASE: A 31-year-old woman underwent a long-treatment protocol for ovarian stimulation. Twenty-seven mature oocytes were obtained, and 21 were fertilized with intracytoplasmic sperm injection. On day 3, 2 cleaved embryos were transferred, but no implantation occurred. The remaining 19 embryos were cryopreserved with the slow freezing method. Three months after oocyte retrieval, 5 frozen day 3 embryos were thawed, the surviving 2 were transferred, but no implantation occurred. Six months after oocyte retrieval, the remaining 14 frozen day 3 embryos were thawed and the surviving 12 cultured. On day 5, 2 embryos reached the expanded blastocyst stage and were transferred, but no implantation occurred. On day 6, 5 of the nontransferred embryos became expanded blastocysts and were cryopreserved again by vitrification. Eight months after oocyte retrieval, 2 recryopreserved day 6 blastocysts were warmed and transferred. Implantation resulted in a dizygotic twin pregnancy. The pregnancy resulted in delivery of normal, healthy male and female infants weighing 2,155 and 2,590 g at birth, at 36 weeks of gestation. CONCLUSION: The blastocysts developed from frozen embryos on day 6 can be recryopreserved by vitrification and have pregnancy potential after warming.