Noninvasive prenatal screening using cell-free DNA.

Noninvasive prenatal screening using cell-free DNA involves analysis of a sample of maternal blood for DNA fragments of fetal chromosomes from the fetal-placental unit to detect common chromosome abnormalities, trisomy 21, trisomy 13, trisomy 18, and sex chromosomes as early as 10 weeks' gestation when the fetal fraction is usually more than 4%. It is the most sensitive and specific prenatal screening option for these conditions. Because it is a screening test, false-positive and false-negative results can occur. Positive screen results necessitate further evaluation for diagnosis to confirm a medical condition, before critical decisions regarding pregnancy are made. Professional organizations provide clinical recommendations to providers regarding prescreen and postscreen counseling and management of results.