Screening for trisomy 21 by fetal nuchal translucency and maternal age: a multicenter project in Germany, Austria and Switzerland.

Objective: To examine the effectiveness of screening for trisomy 21 by a combination of maternal age and fetal nuchal translucency thickness at 10-14 weeks of gestation in Germany, Austria and Switzerland.

Methods: This was a multicenter study of screening for trisomy 21 by a combination of maternal age and fetal nuchal translucency thickness at 10-14 weeks of gestation. All the sonographers involved in the study had received The Fetal Medicine Foundation Certificate of Competence in the 10-14-week scan. Fetal nuchal translucency thickness and crown-rump length were measured in 23 805 singleton pregnancies with live fetuses. In each case the risk for trisomy 21 was estimated on the basis of maternal age and fetal nuchal translucency thickness for crown-rump length with the use of The Fetal Medicine Foundation's software. The distribution of estimated risk was determined and the sensitivity and false-positive rate for a risk cut-off of 1 in 300 was calculated.

Results: Fetal nuchal translucency thickness was successfully measured in all 23 805 pregnancies and outcome was available in 21 959. The median maternal age was 33 (range 15-49) years and in 7935 (36.1%) the age was 35 years or greater. The median gestation at screening was 12 (10-14) weeks and the median fetal crown-rump length was 61 (range 38-84) mm. The estimated risk for trisomy 21 based on maternal age and fetal nuchal translucency thickness for crown-rump length was 1 in 300 or greater in 13.0% (2800 of 21 475) normal pregnancies, in 87.6% (184 of 210) of those with trisomy 21 and in 87.2% (239 of 274) with other chromosomal defects.

Conclusions: In Germany, Austria and Switzerland the results of screening for chromosomal defects by measurement of fetal nuchal translucency thickness, in centers with appropriately qualified sonographers and using The Fetal Medicine Foundation's software, are similar to those reported in the UK using the same methodology.