Turner Syndrome Associated with Cystic Hygroma in One Twin of a Dichorionic Diamniotic Pregnancy: A Unique Case Report

We present a rare case of dichorionic diamniotic twin pregnancy, in which one fetus had Turner syndrome associated with cystic hygroma while the other fetus was phenotypically normal. The pregnancy was terminated due to twin A being alive but with cystic hygroma and twin B having missed abortion. Because it was dichorionic diamniotic with discordant gender, karyotyping was done only on the affected fetus, revealing loss of chromosome X-Turner syndrome. This case highlights that in order to gain a better understanding of the underlying genetic pathways, it is important to send tissue samples for investigation, even for fetuses that appear structurally normal. Dichorionic may not be dizygotic.