Monozygotic twinning after assisted reproductive technologies: a case report of asymmetric development and incidence during 19 years in an international group of in vitro fertilization clinics.

OBJECTIVE: To describe a case of monozygotic twinning with asymmetric development following a single fresh embryo transfer as part of an intracytoplasmic sperm injection (ICSI) treatment. Secondarily, to report the incidence of monozygotic twinning at the IVI (Instituto Valenciano de Infertilidad) clinics.

DESIGN: Case report.

SETTING: Private fertility centers.

PATIENT(S): A 33-year-old woman with a 2-year history of primary infertility.

INTERVENTION(S): Controlled ovarian hyperstimulation and ICSI treatment with single-embryo transfer.

MAIN OUTCOME MEASURE(S): Incidence of monozygotic twinning at the IVI clinics.

RESULT(S): We report a twin pregnancy after a single-embryo transfer. Twins were dichorionic and diamniotic. One fetus had a 6-day delay in its growth compared with the other when observed by ultrasound. Two female infants were delivered, and despite presenting congenital diseases, they were successfully treated and evolved correctly. A subsequent DNA analysis confirmed that the infants were monozygotic. Furthermore, we estimated a monozygotic twinning rate of 1.17% at the IVI clinics, taking into account those cases in which two or more embryos with heart beats were observed by ultrasound scanning after single-embryo transfers.

CONCLUSION(S): Ultrasound scans performed during pregnancy suggested a possible dizygotic origin of the twins, but DNA analysis performed after birth established that they were monozygotic. Genetic analysis is the only valid tool to confirm if like-sex dichorionic twins are monozygotic or dizygotic.