About one in a hundred babies will be born with a birth defect. Most babies with birth defects are born to couples without any known risk factors. However, the risk of birth defects is higher when certain factors are present, such as a personal or family history of birth defects, belonging to certain ethnic groups, maternal age of 35 or older, or having preexisting diabetes. There are a number of tests available that your doctor can use to try and detect birth defects before birth. The use of any of these tests is optional and is a personal choice. However, it is important to know your options for testing. Most testing is covered by insurance, but you should check with your individual carrier for specific testing coverage.
If you have a family or personal history of a genetic defect or an older child with a genetic disorder, or if you will be 35 or older at the time of your delivery, we recommend having genetic counseling. During genetic counseling, you meet with a licensed genetic counselor at the office of one of the perinatal specialists in town who will assess your risks for certain genetic disorders and help you and your partner make a decision about genetic testing options.
There are many types of birth defects. Some are caused by missing or extra chromosomes, called aneuploidy. The most common aneuploidy is a trisomy, a condition where an extra chromosome is present. Down syndrome (Trisomy 21), Edwards’s syndrome (Trisomy 18), and Patau syndrome (Trisomy 13) are some of the more common trisomies. Testing for aneuploidy falls into two categories, screening and diagnostic.
Screening tests are non-invasive, and have no risk for the baby. Screening tests do not tell you if the baby actually has a disorder, only if the risk for the disorder is elevated. For example, your risk of carrying a pregnancy with Down syndrome at age 35 is about 1/270. After screening, your measured risk may be higher or lower than your age related risk. If you hit a certain threshold of risk, you have a positive screening test. If you have a positive test, you will be referred to a genetic counselor, and diagnostic testing will be needed to see if the disorder is actually present. Screening is offered to all individuals, both high and low risk. Screening tests have a risk of both false positive and false negative results.
Diagnostic tests include chorionic villus sampling, amniocentesis, and non-invasive prenatal testing. Diagnostic tests are generally >99% accurate, and provide a diagnosis of a disorder rather than an estimate of risk. The diagnostic tests CVS and amniocentesis are available as a first choice for all pregnant women, including those who do not have risk factors. It should be noted that insurance will generally not cover diagnostic testing unless a woman falls into the “high risk” category for genetic disorders.
These genes can be passed down by parents to their children. Some disorders caused by defective genes are more common in certain ethnic groups, such as sickle cell anemia (African American), cystic fibrosis (non-hispanic white), and Tay-Sachs disease (Ashenazi Jewish, French Canadian, and Cajun descent). Other inherited genetic disorders include Fragile X syndrome (a common cause of mental retardation) and spinal muscular atrophy (a progressive muscle-wasting disorder).
Carrier tests are screening tests that can show if a person carries a defective gene for a certain disorder, such as cystic fibrosis. Carrier tests can be done before or during pregnancy. If you or your partner have a personal or family history of a genetic disorder or belong to a high risk ethnic group, carrier testing may be recommended to you. However, even if you do not have a family history, you can still request carrier testing. Cystic fibrosis is one of the most common inherited genetic disorders; with ~ 1/30 non-Hispanic white individuals carrying a CF gene, and CF testing is offered to all pregnant women.