Hydrops fetalis, thickened placenta and other sonographic findings in a low-level trisomy 21 mosaicism: a case report.

We report a case of trisomy 21 mosaicism detected upon amniocentesis in a 36-year-old woman. Ultrasound examination at 23 weeks' gestation showed a fetus with hydrops, pulmonary hypoplasia, oligohydramnios, thickened placenta, and intrauterine growth retardation. Cytogenetic analysis revealed low-percentage (6%) mosaicism for trisomy 21. Hydrops fetalis and thickened placenta are uncommon findings in fetuses affected by trisomy 21 mosaicism. A short review of the literature is given regarding the sonographic findings associated with trisomy 21 mosaicism, and the genetic counseling in such cases.