ROLE OF PRENATAL ULTRASONOGRAPHY IN WOMEN WITH POSITIVE SCREEN FOR DOWN-SYNDROME ON THE BASIS OF MATERNAL SERUM MARKERS

OBJECTIVE: Our purpose was to evaluate the usefulness of prenatal ultr asonography among women with a positive screen for fetal Down syndrome on the basis of three biochemical markers - maternal serum ol-fetopro tein, human chorionic gonadotropin, and unconjugated estriol. STUDY DE SIGN: A total of 395 women underwent prenatal ultrasonography at a sin gle institution after being identified as screen positive (midtrimeste r risk greater than or equal to 1:195) on the basis of triple-marker s creening between 15 and 18 weeks. Ultrasonographic findings were compa red with the biochemical markers and the eventual fetal outcome for th ese patients. Ultrasonographic abnormalities that were evaluated inclu ded structural defects, nuchal thickening or cystic hygroma, echogenic bowel, cerebral ventricular dilatation, pylectasis, and shortened fem ur. RESULTS: Among 395 patients, 374 (94.7%) had normal karyotype by g enetic amniocentesis (n = 232) or postnatal follow-up (n = 142), 18 (4 .5%) proved to have Down syndrome, and three had other karyotypic abno rmalities. One or more ultrasonographic abnormalities were found in ni ne of 18 (50%) with Down syndrome compared to 27 of 377 (7.2%) other f etuses (p < 0.001). Fetuses with abnormal ultrasonography results incl uded three with other chromosome abnormalities and five with nonchromo somal anomalies. An abnormal ultrasonography result increased the risk of Down syndrome by 5.6-fold (25% from 4.5%) and a negative result re duced the risk by 45% (2.5% from 4.5%). The value of ultrasonography i s further enhanced when all chromosome abnormalities and nonchromosoma l anomalies are considered. CONCLUSION: Abnormal ultrasonographic find ings increase the risk for Down syndrome, whereas normal findings are less predictive of normalcy. After correction for inaccurate menstrual dates, genetic amniocentesis should be offered in spite of a normal u ltrasonography result among women with positive triple screen.