Heterokaryotypic pregnancy: monozygotic monochorionic twins discordant for trisomy 13.

BACKGROUND

The occurrence of a discordant chromosomal abnormality in monozygotic twins is an extremely rare condition.

CASE: We report the prenatal sonographic findings and cytogenetic studies in a monochorionic twin pregnancy discordant for severe fetal anomalies. Amniocenteses demonstrated heterokaryotypia for trisomy 13 in monozygotic twins. The pregnancy was managed conservatively, resulting in the delivery of discordant twins at 32 weeks. The structurally normal twin survived without sequelae, but the abnormal twin died shortly after delivery.

CONCLUSIONS

This report adds to the literature the second known case of a spontaneously conceived monochorionic twin pregnancy discordant for trisomy 13 and highlights the necessity of sampling both fetuses in cases of monochorionic twins presenting with discordant structural anomalies.