First-trimester ultrasound screening for fetal aneuploidies in women over 35 and under 35 years of age.

In a prospective screening study, the utility of the thickness of first-trimester simple hygroma in sonographic screening for fetal chromosomal aberrations was examined. A total of 3380 women, 1280 of whom were 35 years or over, and 2100 of whom were under 35 years, were screened by ultrasound at 9-12 weeks of gestation. The thickness of fetal nuchal simple hygroma was measured. Women over 35 years of age underwent transabdominal chorionic villus sampling (CVS). In women under 35 years of age, CVS was offered only if the thickness of nuchal hygroma was at least 3 mm, or in cases of parental chromosomal abnormalities. A total of 46 chromosomal anomalies were detected, of which 43 (93.5%) showed simple hygroma. The incidence of first-trimester simple nuchal hygroma in pregnancies of women over 35 and under 35 years of age was 5.4% (69 cases) and 1.28% (27 cases), respectively, and the percentage of chromosomal abnormalities was 2.9% and 0.43%, respectively. The risks of trisomies and poor pregnancy outcome were increased at larger sizes of first-trimester simple hygroma. A sensitivity of 93.5% and a specificity of 98.4% of the method were found. Using a measurement of first-trimester simple hygroma of > or = 3 mm to identify pregnancies at risk for chromosomal anomalies at 9-12 weeks of pregnancy is a useful method for selection of women with high and low risk for aneuploidy.