Genetic testing for your baby
“I heard there’s a new blood test available that will check the chromosomes on my baby.” There is a new blood test available to check for some fetal chromosomal problems including Trisomy 13, Trisomy 18 and Trisomy 21. Trisomy 21 is commonly known as Down’s Syndrome. This test is available for high risk women.
Fetal (that baby’s) DNA can be found circulating in maternal(the mom’s) blood. Several companies have developed technologies to allow for testing of the cell free fetal DNA for Trisomy 13, Trisomy 18 and Trisomy 21. These tests can detect over 98% of cases with very small false positive results. However, “a negative free cell fetal DNA test doesn’t ensure an unaffected pregnancy,” ACOG, 2012. These tests only check these three chromosomes, and there might still be a problem with the other chromosomes. These three chromosomes are the most commonly affected.
Fetal sex chromosome testing is available at the same time, allowing parents to know the sex of their baby by 12 weeks of pregnancy.
Who should ask about free cell fetal DNA testing?
- Age 35 or older by time of anticipated delivery
- Previous pregnancy history of Trisomy
- Abnormal ultrasound testing that could indicate Trisomy
- Abnormal first or second trimester screening
- Parental chromosomal disorder increasing aneuploidy risk
What happens if the free cell fetal DNA testing is positive?
- Additional testing can be performed depending on how far along in pregnancy (chorionic villi sampling or amniocentesis)
- Genetic consult can be considered to determine plan of care for pregnancy
Do I need other testing?
- Ultrasound is recommended around 12 weeks of pregnancy to check for nuchal thickness of fetus. This is elevated in some disorders
- AFP testing for open neural tube defects is recommended at 16 weeks in the form of a blood test.
This is one of the tests that you can use to check on the health of your baby. There are others and we will include information regarding these in future posts. Give us a call if you would like to discuss more about these options with your health care provider.
ACOG Committee Opinion Number 545 December 2012