What Does Prenatal Genetic Testing Show?

Prenatal genetic testing (also called prenatal genetic screening) is an optional process that provides information on a fetus’ health or risk for health problems. It involves examining genes (which determine how the body works) or chromosomes (which carry genes). 

Testing the fetus’ genes and chromosomes can identify genetic disorders like spina bifida, Down syndrome, and trisomy 13. Other tests done on parents can determine the baby’s risk of inheriting specific genes and chromosomes from them.  

The results of prenatal genetic testing help parents and doctors make important decisions about the fetus.

Types of Genetic Testing During Pregnancy

There are two types of genetic testing: screening and diagnostic prenatal tests. 

Screening tests

Screening tests provide information on the likelihood of a fetus having genes or chromosomes that cause health issues. These tests don’t diagnose conditions — they assess the risk of developing them. For example, parents can get a blood test that screens for genes that cause conditions like cystic fibrosis, spinal muscular atrophy, or sickle cell disease.

The two main types of blood screening tests are:

• Cell-free fetal DNA testing. Also called non-invasive prenatal testing (NIPT), it assesses small amounts of fetal DNA in the mother’s blood.
• Serum testing. This test checks protein levels in the blood to evaluate the risk for abnormal numbers of chromosomes. 

Specific tests include:

• Alpha-fetoprotein (AFP) screening. Also referred to as maternal serum screening, this test looks for high AFP levels that can indicate potential physical problems with the fetus’s face, abdomen, or spine.
• Quad screen. This blood test measures the levels of four substances that can indicate a risk of chromosomal abnormalities and neural tube defects.
• Nuchal translucency. Using ultrasound, doctors measure the thickness of the fetus’s neck, which provides insight into conditions such as abnormal heart formation. 
• Fetal anatomy scan. This ultrasound procedure looks for problems with the brain, heart, kidneys, abdomen, skeleton, face, legs, and arms.

Diagnostic prenatal tests

Diagnostic prenatal tests determine whether a fetus has certain genetic conditions. There are two main types: amniocentesis and chorionic villus sampling (CVS). 

In amniocentesis, the doctor inserts a needle through the skin into the mother’s uterus and removes a sample of amniotic fluid for analysis. A CVS test involves the doctor getting cells from the uterus either through the abdomen or vagina.

Many parents ask, “What is the earliest time a fetus can be tested for genetic testing?” Providers can perform an amniocentesis between 16 and 20 weeks of pregnancy and a CVS at around 11 to 13 weeks. 

In either case, samples are sent to a lab where several assessments can be performed. They include standard karyotyping, microarray or special panels, and fluorescence in situ hybridization (FISH). It can take up to two weeks for the lab to provide results. 

Prenatal Genetic Testing Is a Personal Choice

Parents decide whether to get prenatal genetic testing. Common reasons to have testing performed include:

• Pregnancy over age 35
• Previous miscarriages or stillbirths
• Personal or family history of genetic conditions
• Abnormal results from screening tests

Learn More About Prenatal Genetic Testing from Baptist Health

If you have questions about prenatal genetic testing, we’re happy to answer them. Our mother and baby care experts can talk with you about the pros and cons of testing and help you decide how to move forward.