Cell-Free DNA Testing in Pregnancy

  • By:  Melissa Waddell

Cell-free fetal DNA (CffDNA) testing is a fairly new way of determining if a pregnant woman’s baby has a chromosomal disorder, such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18) or Patau syndrome (trisomy 13). Cell-free fetal DNA is the genetic material that is released from the placenta and is circulating in a woman’s blood during pregnancy. It starts off in very small quantities in the first trimester and increases throughout the pregnancy. CffDNA can generally reflect the genetic makeup of the developing baby.

The American College of Obstetrics and Gynecology (ACOG) currently recommends CffDNA testing in women who are at an increased risk for trisomy 13, 18, or 21. These risk factors include: advanced maternal age (35 years or older), having an ultrasound that indicates an increased risk of chromosomal abnormality, a previous pregnancy with a trisomy, a positive first or second trimester screening test, or a known balanced chromosome translocation of the mother or father that is associated with trisomy 13, 18, or 21.

Currently ACOG does not recommend this test in low-risk pregnancies because there is not enough data on its use in this population. Routine first and second trimester screening tests are recommended for this group of women. The CffDNA test cannot detect neural tube defects such as spina bifida so that test will need to be done between 15-20 weeks. The cell-free fetal DNA testing can be performed during or after the 10th week of pregnancy and after pretest genetic counseling has been provided. 

The cell-free fetal DNA test is a screening test, not a diagnostic one. Therefore, if the test comes back positive for a chromosomal abnormality, then the baby is at increased risk of having a chromosomal abnormality. In these cases, the performance of more invasive procedure such as chorionic villi sampling (CVS) between the 10th and 12th week of pregnancy or an amniocentesis between 15 and 20 weeks should be offered to fully evaluate the baby’s chromosomes. 

The cell-free fetal DNA testing involves collecting a blood sample from the mother. It is a test that will need to be performed in every pregnancy that is considered an increased risk for chromosomal abnormalities. The CffDNA test can also reveal the sex of the baby and may also screen for sex-linked chromosome abnormalities such as XXX, XXY, XO or XYY. If you do not want to know the sex of the baby, this part can be omitted.

Cell-free DNA testing is also being researched for other uses. For example, circulating cell-free DNA (ccfDNA) is being developed to detect and manage certain cancers that are released into the blood stream. This is referred to as a liquid biopsy. This blood draw could replace an invasive surgical excision or biopsy of the tumor tissue. The clinical utility of ccfDNA has yet to be fully determined, but it has the potential to help distinguish between benign and malignant tumors, determine a likely prognosis, and to monitor the effectiveness of treatment just from drawing a sample of blood.

Who would have imagined that fetal DNA was circulating in the mother’s blood? Or that it could be separated from her blood to allow analysis of the fetus’s genetic makeup? This is an exciting scientific development. These new CffDNA blood tests have great promise, especially if they can be expanded to include broader screening of DNA for more abnormalities. Meanwhile, the currently available tests are only able to detect a few specific abnormalities, and they shouldn’t be used as a screening test for all pregnancies. They are useful in high-risk pregnancies, but abnormal results must still be confirmed by invasive testing. 

 

Melissa Waddell, WHNP, a Hampton Roads native, is a nurse practitioner at Atlantic Ob/Gyn. Please call 757-463-1234 or visit www.atlanticobgyn.com.

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