First-trimester nuchal translucency and maternal serum free beta-hCG and PAPP-A can detect triploidy and determine the parental origin.

Abstract

To evaluate the levels of first-trimester screening markers in triploid pregnancies and to determine the parental origin of triploidy. During the five-year study period, 12322 patients with singleton pregnancies underwent combined first-trimester screening using nuchal translucency (NT) and maternal serum free beta-human chorionic gonadotrophin (free beta-hCG) and pregnancy associated plasma protein-A (PAPP-A) at 10 to 14 weeks' gestation. Maternal serum markers and NT were evaluated in cases of triploidy. Molecular analysis was performed using polymorphic markers to establish the parental source of triploidy. Eight cases of triploidy were detected at a rate of at least 1 in 1540. All cases were electively terminated early in gestation or resulted in spontaneous miscarriage. Two patterns of first-trimester markers emerged: type I, characterized by extremely high levels of free beta-hCG and elevated NT; and type II, characterized by very low levels of PAPP-A and free beta-hCG with normal NT. Molecular analysis demonstrated that type I triploidy is of paternal origin (diandric) and type II is of maternal origin (digynic). On the basis of these results, it may be possible to detect triploid pregnancies in the first trimester and determine their origin using combined first-trimester screening.