Screening for triploidy by fetal nuchal translucency and maternal serum free β-hCG and PAPP-A at 10-14 weeks of gestation

In 25 cases of triploidy at 10–14 weeks of gestation, compared with 947 controls, the median multiple of the median (MoM) fetal nuchal translucency (NT) thickness was significantly increased (1.89 MoM), and maternal serum total and free β‐human chorionic gonadotrophin (hCG) were increased (3.13 MoM and 4.59 MoM respectively), alpha fetoprotein (AFP) was increased (2.14 MoM), and pregnancy associated plasma protein A (PAPP‐A) was decreased (0.12 MoM). There are two types of triploidy. In type I, where the additional chromosome set is of paternal origin, the placenta is partially molar and the fetus is relatively well‐grown. Type II, where the extra chromosome set is of maternal origin, is characterized by a small normal looking placenta and severe asymmetrical fetal growth restriction. In type I triploidy there was increased fetal NT (2.76 MoM), maternal serum total hCG (4.91 MoM), free β‐hCG (8.04 MoM), and AFP (3.22 MoM), and mildly decreased PAPP‐A (0.75 MoM). In type II triploidy fetal NT was not increased (0.88 MoM), and there was a decrease in maternal serum total hCG (0.16 MoM), free β‐hCG (0.18 MoM), PAPP‐A (0.06 MoM) and AFP (0.77 MoM). We conclude that a large proportion of triploidy cases of both phenotypes could be identified in the first trimester using NT, maternal serum free β‐hCG and PAPP‐A with a combination of trisomy 21 risk and an atypicality approach. Copyright © 2000 John Wiley & Sons, Ltd.