Conjoined ischiopagus twins after single euploid embryo transfer: A case report and review of the literature.

We report a case of an exceedingly rare form of conjoined twinning in a 37-year-old patient who underwent a single euploid embryo transfer for severe male factor infertility. The male partner presented with congenital bilateral absence of the vas deferens, absence of the right seminal vesicle, and right renal agenesis. The sperm used to create the couple's embryos were obtained by TESE and cryopreserved with subsequent thawing. The patient had an unremarkable IVF and medicated frozen embryo transfer cycle. The serum βHCG trend was unremarkable, and pregnancy ultrasound revealed a single fetal pole visualized until 8 weeks of gestation, when two fetal poles were noted. A comprehensive ultrasound evaluation at 9 weeks and 6 days revealed monochorionic, monoamniotic ischiopagus conjoined twins. Twin B demonstrated significant skin edema, a large pericardial effusion, and possible abnormal intracranial anatomy. The couple elected to terminate the pregnancy. Monoamniotic, monochorionic twinning is a rare complication after single embryo transfer, with conjoined twinning exceptionally rare. While several mechanisms underlying monochorionic, monoamniotic twinning after single embryo transfer has been proposed, the development of conjoined twins following embryo transfer is poorly understood. Further investigation is needed to understand the underlying pathophysiologic processes responsible for this phenomenon. These data will aid clinicians in counseling, risk-stratifying, and ultimately, managing rare occurrences of conjoined twinning after SET.