Objective: To estimate how many additional chromosomal abnormalities can be detected by diagnostic testing compared with noninvasive prenatal testing in a high-risk prenatal population.
Methods: All karyotype results of invasive prenatal testing in singleton pregnancies performed in response to a positive prenatal screen through the California Prenatal Screening Program from April 2009 through December 2012 were examined. Abnormal karyotypes were categorized as to whether the abnormality is detectable by current noninvasive prenatal testing methods.
Results: Of 1,324,607 women who had traditional screening during the study period, 68,990 (5.2%) were screen-positive. Of screen-positive women, 26,059 (37.8%) underwent invasive diagnostic testing and 2,993 had an abnormal result (11.5%). Of these, 2,488 (83.1%) were predicted to be detectable with current noninvasive prenatal testing methods, and 506 (16.9%) were considered not currently detectable. Trisomy 21 accounted for 53.2% of the abnormal results (n=1,592). Common aneuploidies, detectable by noninvasive prenatal testing, comprised a higher percentage of abnormal results in older women (P<.01).
Conclusion: For pregnant women with a positive aneuploidy screen who pursued diagnostic testing, 16.9% of chromosome abnormalities are not currently detectable by noninvasive prenatal testing. Undetectable aneuploidies range from relatively mild to those associated with significant disability. This is important information to be considered by patients, health care providers, and screening programs in evaluating the use of traditional screening and invasive prenatal diagnosis compared with noninvasive prenatal testing.