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

We report a case of monozygotic twinning with asymmetric development after a single-embryo transfer. We also estimate the incidence of monozygotic twinning in our IVF clinics.


Antonia Tocino, M.D., Víctor Blasco, M.Sc., Nicolás Prados, Ph.D., Manuel J. Vargas, M.D., Antonio Requena, Ph.D., Antonio Pellicer, Ph.D., Manuel Fernández-Sánchez, Ph.D.

Volume 103, Issue 5, Pages 1185-1189



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.


Case report.


Private fertility centers.


A 33-year-old woman with a 2-year history of primary infertility.


Controlled ovarian hyperstimulation and ICSI treatment with single-embryo transfer.

Main Outcome Measure(s):

Incidence of monozygotic twinning at the IVI clinics.


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.


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.

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