Screening for fetal aneuploidies and fetal cardiac abnormalities by nuchaltranslucency thickness measurement at 10-14 weeks of gestation as part of routine antenatal care in an unselected population

Objectives To evaluate first trimester pregnancy screening for fetal aneupl oidy and congenital heart defects by maternal age and nuchal translucency m easurement and screening for fetal aneuploidies and congenital heart defect s by ultrasound in an unselected population. Design A prospective study. Setting Fetal medicine unit, St George's Hospital, London. Sample 4523 consecutive viable fetuses at 10-14 weeks with a crown-rump len gth between 38 and 80 mm were scanned transabdominally (93%) or transvagina lly (7%). Methods Screening was performed by calculating the background risk from mat ernal age, gestational age and obstetric history, which was then adjusted w ith the nuchal translucency measurement in relation to crown-rump length (a djusted risk). Main outcome measures Measurements of crown-rump length and nuchal transluc ency thickness. An adjusted risk of > 1:270 was considered as a positive sc reening test. Pregnancy outcome was obtained through karyotyping, outcome q uestionnaires and examination of the newborn infants. Results Mean maternal age was 29.4 years and mean gestational age 12.2 week s. Screening was positive in 230/4523 fetuses (5.1%), when the adjusted ris k (mean 1:2649) was > 1:270, Fetal karyotype was abnormal in 23 (0.51%) cas es, including twelve with trisomy 21, five trisomy 18, one trisomy 13, one trisomy 10, one monosomy X and two triploidies. For a false positive rate o f 4.7%, the sensitivity of this test was 78% in detecting any fetal aneuplo idy. Only one out of nine major congenital heart defects in this population was found within the 110 euploid fetuses with increased nuchal translucenc y thickness (> 2.5 mm). Conclusion Screening for fetal aneuploidy by maternal age and nuchal transl ucency measurement can be effective in an unselected population. However, o ur results do not support its effectiveness in the detection of cardiac abn ormalities.