Increased Nuchal Translucency and Early Growth Retardation Related to Confined Placental Mosaicism of Trisomy 16 in a Dichorionic Twin.

Confined placental mosaicism (CPM) of trisomy 16 is related to intrauterine growth restriction; however, its association with increased nuchal translucency (NT) has not been sufficiently studied. We report the first case involving a diagnosis of CPM for trisomy 16 in a dichorionic twin. Increased NT (3.7 mm) and 1 week of growth retardation at 12 weeks of gestational age were detected in the affected fetus compared with the normal fetus. Given that the biochemical analytes in maternal serum aneuploidy screening of the abnormal fetus were diluted by the presence of the normal fetus, this method was unreliable as a screening tool. Therefore, in dichorionic twins, ultrasonographic findings such as increased NT and early growth retardation can serve as important indicators for the diagnosis of CPM of trisomy 16.