Sequential screening for trisomy 21 by nuchal translucency measurement in the first trimester and maternal serum biochemistry in the second trimesterin a low-risk population

Objective To evaluate screening for trisomy 21 in a low-risk population uti lizing a combination of nuchal translucency measurement in the first trimes ter and the triple test in the second trimester. Methods This was a retrospective stud), of 9342 women with singleton pregna ncies who booked for delivery in our hospital over a period of 5 years. A n uchal translucency scan was carried out at 10-13 weeks' gestation and for t hose with a measurement of 3.5 mm or more chorionic villus sampling was per formed. All other women were asked to return for the triple test at 16 week s' gestation. Amniocentesis was offered to women in whom the nuchal translu cency was 2.5-3.4 mm, the triple test showed a risk of greater than or equa l to 1 : 250 and in women aged greater than or equal to 35 years. Results The detection rate using the combined screening method was 95% (18/ 19) with a screen-positive rate of 7.2 %. In comparison, screening by mater nal age alone would have identified nine (47%) trisomy 21 pregnancies with a screen-positive rate of 10.7%. Conclusion Our data suggest that the combination of nuchal translucency mea surement in the first trimester and the triple test in the second trimester is associated with a very high detection rate of trisomy 21 at a relativel y low screen-positive rate.