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Cell-Free DNA Test

British Columbia Specific Information

In British Columbia, prenatal and newborn screening is offered free to all families.

During your pregnancy, your health care provider will offer prenatal screening. Prenatal screening can tell you your chance of having a baby with birth defects. The tests can consist of one or more blood tests and ultrasound. These tests are ordered by your health care provider and can be done at any hospital or laboratory. For more information on prenatal genetic screening, visit BC Women’s Hospital & Health Centre – Prenatal Screening and Perinatal Services BC - Prenatal Genetic Screening Program.

During the first few days after birth, your baby will have a newborn screening test, which includes a blood test and examination by a doctor or midwife. Early detection and treatment of some disorders can help prevent severe mental handicap, growth problems, health problems, or even sudden infant death. For more information on newborn screening, see HealthLinkBC File #67 Newborn Blood Spot Card Screening or visit Perinatal Services BC - Newborn Screening.

Test Overview

Cell-free fetal DNA is a screening test to look for certain birth defects in a fetus. It's done to find birth defects caused by an abnormal number of chromosomes. It also can reveal the sex and blood type of the fetus.

This is a blood test for the mother. The test can be done as early as 10 weeks in the pregnancy.

If this screening test is positive, it means there is a chance your baby has a birth defect. In that case, your doctor may suggest that you have a diagnostic test, which can show if there is a birth defect.

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Why It Is Done

The test is used to look for birth defects caused by too many or too few chromosomes, such as trisomy 18 and Down syndrome (trisomy 21).

Learn more

How To Prepare

In general, there's nothing you have to do before this test, unless your doctor tells you to.

How It Is Done

A health professional uses a needle to take a blood sample, usually from the arm.

How It Feels

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Risks

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Results

The fetal DNA will be looked at to see if there are missing or extra chromosomes. If there is an extra or missing chromosome (a positive result), your baby may have a chromosomal birth defect. A negative result means that your baby is unlikely to have one of the birth defects this test looks for.

This test can find up to 99% of trisomies such as 18 and 21. That means that it will find these birth defects up to 99 times out of 100 and won't find them 1 time out of 100.footnote 1

References

Citations

  1. American College of Obstetricians and Gynecologists (2016). Screening for fetal aneuploidy. ACOG Practice Bulletin No. 163. Obstetrics and Gynecology, 127(5): e123–e137. DOI: 10.1097/AOG.0000000000001406. Accessed April 6, 2017.

Credits

Current as of:
June 16, 2021

Author: Healthwise Staff
Medical Review:
Kathleen Romito MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Siobhan M. Dolan MD, MPH - Reproductive Genetics