Second Trimester: Cell-free Fetal DNA
Also known as: Noninvasive prenatal testing (NIPT) or noninvasive prenatal diagnosis (NIPD)
Cell-free fetal DNA (cffDNA) testing is a non-invasive maternal blood test that can assess the risk of a pregnant woman's developing baby (fetus) having certain chromosome disorders early in pregnancy. The test requires only a blood draw from a pregnant woman's arm and can be done as early as the 10th week of pregnancy, with results available in about one week. The blood sample is evaluated for fetal cell-free genetic material that circulates in the mother's blood.
Currently, the test primarily screens for three disorders in a developing baby resulting from the presence of an extra chromosome (trisomies): Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). It may also be used to identify other rare conditions resulting from an extra chromosome or missing piece of chromosome (microdeletion).
Studies of cffDNA have shown an ability to recognize 98% of cases of Down syndrome, with a false-positive rate of less than 0.5%. The current first trimester screen only assesses risk of Down syndrome and Edwards syndrome, whereas cffDNA screens for three trisomy disorders with the potential for more.
The American College of Obstetricians and Gynecologists (ACOG) recommends that pregnant women discuss the risk and benefits of prenatal screening with their healthcare practitioners and/or a genetic counselor. Conventional screening such as second trimester maternal serum screening remains the best choice for women with a low risk of having a baby with a chromosome disorder, says ACOG. However, any woman may choose to have cffDNA testing done regardless of her risk.
ACOG recommends that cffDNA testing be offered, after pre-test genetic counseling, to pregnant women at increased risk. They include women age 35 and older, women with a history of a pregnancy with a child with a trisomy, and women carrying a fetus with ultrasound findings indicating increased risk.
Women should make this choice with a thorough understanding of the limitations of the test. CffDNA will detect only the most common trisomies. False-positives and false-negatives do occur. A negative result does not necessarily mean that a woman will have an unaffected child. Women with positive cffDNA results should be referred for genetic counseling and be offered chorionic villus sampling (CVS) or amniocentesis to confirm the diagnosis.