First-trimester genetic diagnosis: a series of six cases

A first-trimester screen consists of a nuchal translucency (NT) ultrasound measurement as well as maternal serum testing for pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG). An increased nuchal translucency (NT) thickness at 11 to 14 weeks gestational age is a common finding for Down syndrome, Trisomy 18 and cardiac defects. We present a series of six patients, four with NT measurements greater than the 95th centile, and two additional cases where the NT was normal, but maternal serum biochemical markers were unusual. All six of these cases had a chromosome anomaly or another genetic condition: Noonan syndrome, triploidy, Down syndrome, Trisomy 18, Turner syndrome and a rare chromosome abnormality known as Ring 18-Monosomy 18. Our series underlines the fact that it is important to explore other genetic and chromosome abnormalities, in addition to Down syndrome and Trisomy 18, when there is an abnormality on a first-trimester screen.