Screening for Down's Syndrome by Measuring Fetal Nuchal Translucency Thickness
Ron Maymon, Eli Dreazen, Zwi Weinraub, Ian Bukovsky, Arie Herman
Ultrasound Unit, Dept. of Obstetrics and Gynecology, Assaf Harofeh Medical Center, Zerifin, and Sackler Faculty of Medicine, Tel Aviv University
Increased fetal muchal translucency (NT) thickness at 10-14 weeks of gestation may indicate underlying fetal chromosomal abnormalities, anatomical anomalies and genetic syndromes. Between January 1997 and May 1998, 1400 women 10-14 weeks pregnant underwent sonographic screening for detection of Down's syndrome (DS). Follow-up was complete in 1208 (86%).
Maternal age ranged from 17-44 years (mean 18.0). 87% were found by screening to have a higher risk (1:380) for DS diagnosed at birth. All these fetuses were karyotyped and 8 had chromosomal abnormalities. 2 fetuses with normal NT were diagnosed later as having DS, 1 by the mid-gestation triple test and 1 by amniocentesis because of advanced maternal age.
Thus sonographic screening identified 8 out of 10 fetuses found to have chromosomal abnormalities at birth. Neonates not karyotyped before birth had no traits at birth that justified chromosomal analysis. Results of this study suggest that NT measurement, combined with maternal age, is an effective 1st trimester screening method for DS in an unselected obstetric population.