Prenatal cell-free DNA (cfDNA) screening is a method of screening for certain chromosomal abnormalities in the fetus. Fetal “cell-free” nucleic acids (DNA and RNA) are found in the maternal circulation, are unique to the current pregnancy, and are thought to be from the placenta. Circulating cfDNA is taken from the plasma of maternal whole blood. Testing is available to detect fetal aneuploidies for chromosome 21, 18, and 13. The test can also determine X and Y chromosomes. This noninvasive test can be performed as early as 10 weeks’ gestation with results available in 1 week. ACOG recommends that women, regardless of age, be offered prenatal screening for aneuploidy by screening or invasive testing. cfDNA testing is one method of noninvasive screening for women at risk for aneuploidy. It is not recommended as a screening test for low-risk women at this time due to lack of testing in the low-risk population.

Indications for cfDNA testing for aneuploidy:

• Maternal age of 35 years or older at delivery

• Ultrasound findings of fetus indicating increased risk for aneuploidy

• Prior history of pregnancy with trisomy

• Positive first- or second-trimester sequential or integrated screen or quad screen

• Parental balanced Robertsonian translocation with increased risk of fetal trisomy 13 or trisomy 21

1. Explain that the test analyzes the relative amount of 21, 18, 13, and Y chromosomal material in circulating cfDNA from a maternal blood sample.

2. Obtain a blood draw with 2 × 10 mL mottled black/tan-topped cfDNA blood collection tubes. Label specimen with the patient’s name, date, and test(s) ordered.

1. Test detects fetal chromosomal 21, 18, and 13 aneuploidies and the presence of the Y chromosome in singletons, twins, and higher order multiple pregnancies.

2. A negative test does not ensure an unaffected pregnancy.

3. A patient with a positive test should be referred to genetic counseling and offered invasive testing to confirm results.

4. cfDNA testing does not replace diagnosis with CVS or amniocentesis.

Pretest Patient Care

1. Discuss family history with the patient to determine whether patient should be offered other forms of prenatal screening or invasive testing depending on the genetic syndrome. Pretest counseling should include the discussion that cfDNA is not a diagnostic test but has a high sensitivity and specificity.

2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Normal

• Negative test indicates no evidence of aneuploidies for 21, 18, or 13.