Prenatal diagnosis and management of monozygotic twins discordant for turner syndrome.

Discordance for Turner syndrome in monozygotic (MZ) twins, which is known as heterokaryotypia, is very rare in MZ pregnancies. The combined effect of idiochromosome loss due to an anaphase lag and the relocation of discordant blastomeres may trigger the twinning procedure and discordance of Turner syndrome. We present 2 cases of MZ twins discordant for Turner syndrome that were diagnosed prenatally by ultrasound and cytogenetic studies (one fetus was 45,X and the other 46,XX). Both cases, which involved monochorionic (MC) diamniotic twins, underwent selective feticide and had favorable outcomes for the remaining twin. Ultrasound, amniocentesis of both sacs (dual amniocentesis) and zygosity determination are indispensable in diagnosing heterokaryotypia. Selective feticide is a treatment option in cases of heterokaryotypic MC diamniotic twins, and in our cases, it resulted in favorable outcomes for the remaining twin.