Prenatal diagnosis of diverse chromosome abnormalities in a population of patients identified by triple-marker testing as screen positive for Down syndrome.

Abstract

Our purpose was to determine the incidence of all types of chromosome abnormalities (i.e., trisomy 21 and other abnormalities) in women receiving prenatal chromosome analysis after a Down syndrome screen-positive result by maternal serum triple-marker testing (alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol analyses). A total of 11,434 patients between 15.0 and 21.9 weeks' gestation received second-trimester Down syndrome risk evaluation by triple-marker testing. By use of a 1:270 midtrimester Down syndrome risk cutoff value, and after ultrasonographic confirmation of gestational age, 677 patients were screen positive for Down syndrome (corrected screen-positive rate 5.92%). Karyotypes were reviewed for 468 (69%) of these patients who received prenatal chromosome analysis. In addition to 12 cases of Down syndrome, 12 other fetal chromosome abnormalities were found (i.e., 5.13% had a chromosome abnormality of some type). Expressed as a proportion of all patients with a corrected Down syndrome screen-positive result, at least 3.69% had a chromosome abnormality. The overall spectrum of abnormal karyotypes (approximately 50% autosomal trisomy, 25% structural and 25% sex chromosome abnormality) appears to be comparable to that seen in patients undergoing amniocentesis because of advanced maternal age. As is the case for women of advanced maternal age, preamniocentesis counseling for patients with positive triple-marker testing results should reflect the relatively high probability that an abnormality other than Down syndrome may be identified.