Urine hyperglycosylated hCG plus ultrasound biometry for detection of Down syndrome in the second trimester in a high-risk population

Objective: To evaluate measurement of levels of urine hyperglycosylated hCG, a form of hCG with abnormally branched oligosaccharide side chains, in conjunction with ultrasound biometry for Down syndrome risk prediction in an at-risk group. Method: We prospectively measured urine hyperglycosylated hCG levels, humeral length, and nuchal thickness in women who had second-trimester amniocentesis. Urine hyperglycosylated hCG levels were measured by a two-step enzyme-immunometric assay using monoclonal antibody beta 152. Humeral length, nuchal thickness, and hyperglycosylated hCG values were expressed as multiples of the median, and the Down syndrome screening efficiency of the three analytes plus age was determined. A receiver operating characteristic (ROC) curve was generated, and the area under the curve was used to assess the Down syndrome screening performance of the algorithm. Results: There were 23 cases of Down syndrome among 1016 singleton pregnancies. Mean gestational age (+/- standard deviation) was 16.1 +/- 1.2 weeks at the time of amniocentesis. Mean maternal age was 37.1 +/- 3.2 years. Biometry and measurement of hyperglycosylated hCG levels had a 91.3% detection rate at a 3.2% false-positive rate and a 100% detection rate at a 10.7% false-positive rate. The area under the ROC curve was 0.986 (P < .001), and that for measurement of hyperglycosylated hCG levels plus age was 0.941 (P < .001). The area under the curve was significantly larger with combined biochemical and biometry markers compared with measurement of hyperglycosylated hCG levels plus age alone (P < .02), proving that the former was superior to the latter. Conclusion: A new Down syndrome biochemical marker combined with ultrasound biometry had a high screening efficiency in a high-risk group. All cases of Down syndrome in this study population would have been detected at an amniocentesis rate of less than 10.7%. Our results appear superior to those found with other second-trimester algorithms. The combination is promising as an alternative to "automatic" genetic amniocentesis in women of advanced maternal age and other high-risk groups. (Obstet Gynecol 2000;95:889-94. (C) 2000 by The American College of Obstetricians and Gynecologists).