Case Report: Monochorionic triamniotic triplet pregnancy following single vitrified-warmed blastocyst transfer

Monochorionic triamniotic triplet pregnancy following single embryo transfer is an exceptionally rare outcome of assisted reproductive technology. We report a monochorionic triamniotic triplet pregnancy following transfer of a single vitrified-warmed blastocyst. Fertilization was performed by intracytoplasmic sperm injection, with no assisted hatching, trophectoderm biopsy or preimplantation genetic testing. Initial transvaginal ultrasound 21 days after embryo transfer demonstrated a singleton intrauterine pregnancy. At 8 weeks and 1 day of gestation, three viable embryos were identified within a monochorionic triamniotic pregnancy. The pregnancy remained uncomplicated, with appropriate growth of all three fetuses, and three live female infants were delivered at 35 weeks of gestation. This case adds to the limited number of reported monochorionic triamniotic triplet pregnancies following single embryo transfer and is distinguished by transfer of a day-6 vitrified-warmed blastocyst that re-expanded from grade 2BB after warming to 6BB before transfer, without assisted hatching, trophectoderm biopsy or preimplantation genetic testing.