A successful birth of healthy monozygotic dichorionic diamniotic (DD) twins of the same gender following a single vitrified-warmed blastocyst transfer.

Purpose: To report the world's first case of live monozygotic dichorionic diamniotic (DD) twins after a single vitrified-warmed blastocyst transfer in a cycle during which hormone supplements were given.

Methods And Results: The patient was a 39-year-old woman with tubal factor infertility. Six oocytes were retrieved and three blastocysts were vitrified after insemination with her husband's sperm. Two months later, a single warmed blastocyst was transferred on the fifth day after progesterone supplementation during the luteal phase. Two gestational sacs and fetuses with heartbeats showing lambda sign under ultrasonography were recognized at 7 weeks of gestation and the patient gave birth to two female infants at gestational 33 weeks. The pathological examination demonstrated that the DD twin placentas fused in the third trimester.

Conclusions: This report suggests that the splitting of the transferred embryo took place after the blastocyst stage and the popular credo that the timing of embryo division governs the placental configuration of monozygotic twins (MZT) must be re-examined as to its veracity.