INCREASED NUCHAL TRANSLUCENCY AS A MARKER FOR FETAL CHROMOSOMAL DEFECTS

Background Screening for trisomy 21 (Down's syndrome) by measuring mat ernal serum alpha-fetoprotein, chorionic gonadotropin, and estriol con centrations and then performing chorionic-villus sampling or amniocent esis identifies approximately 60 percent of fetuses with this disorder . We used ultrasonography to detect increased nuchal translucency and cystic hygroma, which are characteristic features of fetuses with chro mosomal defects. Methods We performed transvaginal ultrasonography in 10,010 unselected adolescents and women less than 40 years of age with live singleton fetuses at 10 to 15.9 weeks of gestation. Increased fe tal nuchal translucency was defined as an area of translucency at leas t 3 mm in width, and cystic hygromas were defined as septated, fluid-f illed sacs in the nuchal region. Subjects whose fetuses had these find ings were offered fetal karyotyping. Information on pregnancies, deliv eries, and neonates was subsequently obtained from hospital records an d national birth and malformation registries. Results Nuchal transluce ncy or cystic hygroma was seen in 76 fetuses (0.8 percent), of which 1 8 (24 percent) had an abnormal karyotype. The sensitivity for trisomie s 21, 18, and 13 combined was 62 percent (13 of 21 fetuses), and the s ensitivity for trisomy 21 alone was 54 percent (7 of 13 fetuses). Conc lusions The use of transvaginal ultrasonography to detect increased nu chal translucency and cystic hygroma is a sensitive test for fetal ane uploidy. It can be done earlier in pregnancy than serum screening, and it decreases the subsequent need for chorionic-villus sampling or amn iocentesis. (C) 1997, Massachusetts Medical Society.