What is genetic testing (carrier screening)?
Genetic testing is when a blood test is given to prospective or expecting parents to look for abnormal genes that can lead to certain diseases in their baby. Most genetic diseases are known as "recessive disorders," which means that each parent needs to pass along an affected gene to the baby in order for the child to be affected. In other words, if you screen positive for a genetic abnormality but your partner does not, your child will not inherit the condition. And even if you both screen positive, there's only a 25 percent chance your baby will have the disease.
You can get a carrier screening at your ob-gyn's office with a single blood test; you typically receive the results in two weeks. Most often, a woman is tested first (only because you're more likely to see your doctor regularly if you're in trying-to-conceive mode) and if those results don't show a problem gene, her partner usually doesn't need to be tested.
When should you get genetic testing?
Genetic testing is ideally done before you start trying to get pregnant, says Angela Trepanier, MS, CGC, co-director of the genetic counseling program at Wayne State University and president of the National Society of Genetic Counselors. "But because so many pregnancies are unplanned, many couples get screened early in pregnancy," she says.
Getting screened before you try to get pregnant can give you reassurance (if you or your partner is not a carrier, it's one less thing to worry about when do you get pregnant) or can help you make an informed game plan for pregnancy. If it turns out that you are both carriers, you can be prepared for and bone up on what it means to have a baby with the genetic condition, choose to learn about certain prenatal tests to check whether your baby's healthy, or you can consider other options like egg or sperm donation or adoption.
Getting tested once you become pregnant (if you hadn't done so ahead of time) can help you and your doctor decide the right prenatal tests for your baby, and what to look for if you choose to have them. If you know that your baby's at an increased risk for having cystic fibrosis or sickle cell disease, for instance, your doctor can look for those conditions specifically through either a CVS (chorionic villi sampling) or amniocentesis.
Who should get genetic testing?
Your ethnic background and family history are the main factors that determine whether or not genetic testing is right for you. "That's because the diseases for which genetic testing is currently offered tend to be more common among certain ethnic groups," says Trepanier. Here's an example of groups who are more likely to have certain genetic diseases.
- European Caucasians and Eastern European Jews face an increased risk of cystic fibrosis.
- Eastern European Jews also face an increased risk of conditions like Tay-Sachs, Canavan, and familial dysautonomia.
- African Americans and people of Mediterranean descent (Greeks, Turks, Italians) face an increased risk of conditions like sickle cell anemia and thalassemia. People of Southeast Asian descent also face an increased risk of thalassemia.
- French Canadians face an increased risk of Tay-Sachs and cystic fibrosis.
Though there are many other recessive genetic diseases, they are not routinely checked for because they're either very, very rare or because the right tests have not been developed yet, says Trepanier.