Screening for fetal trisomies by maternal age and fetal nuchal translucency thickness at 10 to 14 weeks of gestation.

Objective: To evaluate screening for chromosomal defects by a combination of fetal nuchal translucency thickness and maternal age.

Methods: A prospective multicentre screening study where fetal nuchal translucency thickness was measured at 10 to 14 weeks of gestation. Methods: 20,804 women with singleton pregnancies screened at 10 to 14 weeks of gestation from 1 September 1992 to 28 October 1994. Methods: Trisomy 21 and other chromosomal defects identified by increased nuchal translucency thickness and by a combination of nuchal translucency thickness and maternal age.

Results: In normal fetuses nuchal translucency thickness increased significantly with crown-rump length. The nuchal translucency was above the 95th centile in 77% (66 of 86) of fetuses with trisomy 21 and in 78% (61 of 78) of those with other chromosomal defects. On the basis of the distribution of nuchal translucency measurements in normal fetuses and those with trisomy 21, a new method of screening is proposed which involves assessment of individual risk based on the combination of fetal nuchal translucency, crown-rump length and maternal age. The minimum risk was 1/100 in 4.9% of the normal pregnancies, in 80% of those with trisomy 21 and in 77% of those with other chromosomal defects.

Conclusions: Screening for fetal trisomy 21 can be carried out effectively during the first trimester of pregnancy.