Everyone has two sets of DNA: one from Mom and one from Dad. When a sperm (carrying Dad’s DNA) fertilizes an egg (containing Mom’s DNA), those two sets of DNA combine to make a new mixture which builds the unique genetics of your baby. Your baby’s genetics will determine your child’s hair and eye color, height, and all sorts of other traits.

A genetic disease occurs when one or both parents’ sets of DNA have a mutation (a change from the usual), which could make a baby more prone to developing health conditions. Some mutations are harmless, some only slightly boost the risk of a condition, and others can cause more serious diseases or developmental problems that can begin at birth.

Just about everyone carries a gene for at least one genetic disorder even if it has never shown up in your family history. If you have a mutation in just one set of genes, you are what is known as a “carrier”: You are carrying the genes for a genetic disorder but have no signs of the disease.

Rarely, a condition (like Huntington’s disease) can be caused by a mutation in just one set of DNA from one parent. But in most cases, including cystic fibrosis and sickle cell disease, it takes a mutation in both sets of DNA, one from Mom and one from Dad, for a child to be affected by a genetic disease. Therefore, these diseases are rare.

A carrier screening tests whether you or your partner is a carrier for certain genetic diseases. It is a swab test, which requires a quick swab on the inside of your cheek. If both you and your partner are carriers, and you both pass the mutation-carrying DNA along to a baby, the baby could end up with a full-fledged version of the disease. This test determines the likelihood of this happening.

Parents can be tested for some of genetic disorders before (which is preferable) or during pregnancy, thanks to genetic testing. In almost all cases, testing is recommended for one parent. Testing the second parent only becomes necessary if the first tests positive.

In the past, the American Congress of Obstetricians and Gynecologists (ACOG) only recommended carrier screenings to parents of certain ethnic or geographic backgrounds considered more at risk of specific disorders. However, some conditions are not limited to one ethnicity. Today’s environment we have many people are of mixed ethnic backgrounds, which means it can be hard to make recommendations based on an ethnic or geographic basis. Although they are still very rare, some genetic conditions are common enough that practitioners should offer to screen for them in every patient. 

Because some people are more likely to carry specific genetic mutations, your doctor may recommend a number of other screenings based on your family heritage and/or medical history:

• Eastern and Central Eastern (Ashkenazi) Jewish descent: 
  Tay-Sachs disease, Canavan disease and familial dysautonomia; there are several other disorders some practitioners screen for including Bloom syndrome, Maple syrup urine disease and Niemann-Pick disease, among others
• French-Canadian or Cajun: Tay-Sachs disease
• Ovarian insufficiency syndrome: Fragile X syndrome; the screening should also be offered to women with a family history of fragile X-related disorders
• Other family history of disease: Anyone who has a family history of genetic diseases such as a cousin who had Tay-Sachs disease, for instance, should be screened for those diseases as well, as they’re more likely to be a carrier

Expanded carrier screening now enables all couples, regardless of their ethnic or geographical profile, to test for a broad array of genetic conditions before conceiving. It can screen for the carrier gene of hundreds of diseases, giving you the power of knowing whether you and your partner are at risk of passing along any of these genetic conditions to a baby you conceive together.

ACOG has specific recommendations for which disorders practitioners should include in an expanded carrier panel. Conditions should occur in at least 1 in 100 people, reduce the quality of life, impair cognitive or physical abilities, require surgical or medical intervention, and have an onset in childhood. Here are a few of the most common diseases expanded carrier screenings test for:

• Alpha-Thalassemia
• Beta-Thalassemia
• Cystic Fibrosis
• Familial Hyperinsulinism
• Fanconi Anemia Group C
• Fragile X Syndrome
• Gaucher Disease
• Glycogen Storage Disease Type 1a
• Maple Syrup Urine Disease Type 1A/1B
• Neimann-Pick Disease Type A/B
• Sickle Cell Disease
• Spinal Muscular Atrophy (SMA)
• Tay-Sachs Disease

If you’re interested in testing for specific diseases, talk to your practitioner about your and your partner’s risk factors, as well as how you’ll use the information about each disease. If you have further questions, a conversation with a genetic counselor can be helpful.

Both ACOG and the American College of Medical Genetics and Genomics (ACMG) agree that all couples should be offered the option of carrier screening, should they choose. To reduce the potential emotional downside of screening, experts recommend that couples have a discussion with an OB/GYN and/or genetic counselor before getting the testing to make sure they understand what is being tested for. Any discussion about carrier screening should also include a conversation about what you would do if these results come back positive. You can choose to opt-out of any or all carrier screenings or request not to receive certain results. Ultimately, it’s up to you and your partner to make an informed decision about what’s best for you and your soon-to-be growing family.