Is maternal plasma DNA testing impacting serum-based screening for aneuploidy in the United States?

April 2 , 2015 GIM article: Is maternal plasma DNA testing impacting serum-based screening for aneuploidy in the United States?

In 2012, the American Congress of Obstetricians and Gynecologists (ACOG) recommended that next-generation sequencing of maternal plasma for fetal aneuploidy be offered as a secondary screening option to women already identified as having a high risk pregnancy. However, some commercial labs are extending the offering as a main screening option to even women with low risk pregnancies. With more people using the maternal plasma DNA testing, are the rates of routine serum screening being reduced?

“Results:The 82 laboratory survey results available for comparison showed that 1.7 million women were screened in 2014, a 5% increase over 2011. In the two screening laboratories, the proportion of screened women age 35 and older increased for several years but then experienced reductions of 8 and 18% by mid-2014 when compared with the highest rates observed.”

“Conclusion: As of 2014, maternal plasma DNA testing appears to have had only a minor impact on serum screening rates in the United States. Ongoing surveillance has the potential to determine if, and when, DNA testing begins to replace serum testing as a primary screen for Down syndrome in the United States.”

“Given the inevitable pressure to offer DNA testing as a primary screening test, research into patient and provider education, predictive values in the general population, handling of test failures/no-calls, and other practical issues surrounding the expansion of services to the broader pregnancy community should become high priorities.”

So it turns out that increased uptake of maternal plasma DNA testing has not resulted in a reduction of routine serum screening. But why?

“Together, these data are consistent with little, if any, reduction in the total numbers of women having serum screening in the United States and with a small but consistent reduction in the proportion of women age 35 and older having serum screening. If several hundred thousand DNA tests are being performed, then who is being tested? Some are women age 35 and older who previously opted for serum screening; others would previously have chosen an invasive procedure without any screening, and some may have not had any prenatal testing for aneuploidies. Additionally, some DNA testing is being performed in women younger than age 35 after a positive serum screening test for chromosomal trisomies. Several of these commercial companies will allow low-risk women to be tested, and this may also contribute to the DNA testing numbers, especially among women who would normally accept serum screening even with its relatively high false-positive rate and low positive predictive power. Taken together, these actions could account for the large number of women choosing DNA testing as well as a reduction in women age 35 and older being tested, while still having little or no impact on overall serum screening rates.”

Palomaki, Glenn E., Edward R. Ashwood, Robert G. Best, Geralyn Lambert-Messerlian, and George J. Knight. 2015. “Is Maternal Plasma DNA Testing Impacting Serum-Based Screening for Aneuploidy in the United States?” Genetics in Medicine, April. doi:10.1038/gim.2015.39.