see A single center’s experience with noninvasive prenatal testing
The rapid uptake of noninvasive prenatal testing (NIPT) has changed patterns of prenatal testing and created complicated genetic counseling scenarios at at least one university-based prenatal diagnosis unit. In a descriptive assessment of the changes brought on by routine use of NIPT in high-risk pregnancies, researchers from the University of North Carolina at Chapel Hill report an unanticipated number of “unclassified” results and higher-than-expected numbers of both false-positive and false-negative results in fetal aneuploidy testing. The sensitivity for detection of aneuploidy in chromosomes 21, 18, and 13 in this clinical setting was lower than that achieved in previous published studies performed in controlled research settings. The current team evaluated results obtained from NIPT aneuploidy tests performed beginning in January 2012, when the test was first offered to pregnant women of advanced maternal age or who had additional risk factors for chromosomal abnormalities. The center tested 208 women over the study period, which ended in September 2012. NIPT detected eight cases of aneuploidy and an additional five cases of “unclassified” abnormal results—an unclassified rate of 11.1%, as compared with 2.8% in prior studies. In three morbidly obese patients, NIPT yielded no result, due to insufficient fetal DNA sample. A false-positive result was obtained in a patient subsequently diagnosed with cancer. Several patients with abnormal ultrasound findings declined invasive testing, opting instead for NIPT. In two of these patients, the NIPT result was normal, yet they delivered neonates diagnosed with aneuploidy. The authors conclude that their findings highlight the importance of counseling patients that NIPT is merely a screening test that does not replace diagnostic testing with amniocentesis or chorionic villus sampling, and that normal NIPT results do not necessarily mean that no other genetic abnormalities are present. —Karyn Hede, News Editor
