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 combinati on of fetal nuchal translucency thickness and maternal age. Design A p rospective multicentre screening study where fetal nuchal translucency thickness was measured at 10 to 14 weeks of gestation. Subjects 20,80 4 women with singleton pregnancies screened at 10 to 14 weeks of gesta tion from 1 September 1992 to 28 October 1994. Main outcome measures T risomy 21 and other chromosomal defects identified by increased nuchal translucency thickness and by a combination of nuchal translucency th ickness and maternal age. Results In normal fetuses nuchal translucenc y 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 chromosoma l defects. On the basis of the distribution of nuchal translucency mea surements in normal fetuses and those with trisomy 21, a new method of screening is proposed which involves assessment of individual risk ba sed 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 p regnancies, in 80 % of those with trisomy 21 and in 77% of those with other chromosomal defects. Conclusion Screening for fetal trisomy 21 c an be carried out effectively during the first trimester of pregnancy.