First trimester screening for aneuploidy: may combined test and fetal DNA work together?

Introduction: The purpose of the study was to evaluate the screening performance of combined test (based on the measurement of nuchal translucency, pregnancy-associated plasma protein A, free β-human chorionic gonadotropin, and maternal age) and fetal DNA screening (NIPS) for trisomies 21 (T21), 18 (T18), and 13 (T13).

Material And Methods: Women who accepted screening had a first-trimester combined test (pregnancy-associated plasma protein A, free β-human chorionic gonadotropin, nuchal translucency interpreted with maternal age) and fetal DNA.

Results: Among 302 women screened (including 4 with affected pregnancies), our study demonstrated that DNA screening for trisomies 21, 18, and 13 achieved a detection rate of 100% with a false-positive rate of 0.02%, overcoming the traditional combined test with 75% of sensitivity and 4.7% of false-positive rate. In particular, fetal DNA may be useful in case of intermediate risk, in order to avoid invasive diagnostic procedures such villocentesis and amniocentesis. Because of fetal DNA costs, it can be used in clinical practice as a second step screening in case of intermediate or high risk at combined test.

Conclusion: Fetal DNA screening may be successfully implemented in routine care, achieving a high detection rate, low false-positive rate, and, consequently, greater safety with fewer invasive diagnostic tests than other methods of screening.