Genetic and chromosomal conditions


  • Genes and chromosomes sometimes change or have missing or extra parts. This can cause serious health conditions and birth defects in your baby.

  • You can have tests before and during pregnancy to find out of your baby is at risk for or has certain genetic conditions and birth defects.

  • A genetic counselor can help you understand test results and how genetics, birth defects and other medical conditions run in families.

  • Your family health history can help you, your provider and your genetic counselor identify genetic conditions that run in your family.

What are genes and chromosomes?

Genes are part of the cells in your body. They store instructions for the way your body grows, looks and works. Your genes make you the way you are — they help control things like your height, the curliness of your hair and the color of your eyes. You inherit (get) genes from your parents. 

Sometimes the instructions in genes change. This is called a gene change or a mutation. You can pass gene changes to your children. Sometimes a gene change can cause health conditions, like cystic fibrosis and sickle cell disease. A gene change also can cause birth defects, like heart defects. These are called single gene disorders, and they run in families. A birth defect is a health condition that is present in a baby at birth. Birth defects change the shape or function of one or more parts of the body. They can cause problems in overall health, in how the body develops or in how the body works.

Chromosomes are the structures in cells that hold genes. Each person has 23 pairs of chromosomes, or 46 in all. For each pair, you get one chromosome from your mother and one from your father. Just like genes, sometimes chromosomes change. There may be too many or too few chromosomes, or part of a chromosome may be missing. These changes can cause chromosomal conditions in a baby. One of the most common chromosomal conditions is Down syndrome (when there are three copies of chromosome 21). Parents can pass chromosome changes to their children, or they can happen on their own as cells develop. 

Any condition related to genes or chromosomes can be called a genetic condition. 

What is genetic counseling?

Genetic counseling helps you understand how genes, birth defects and other medical conditions run in families, and how they can affect your health and your baby's health. You get genetic counseling from a genetic counselor. This person is trained to know about genetics, birth defects and other medical problems that run in families. She can help you understand the causes of genetic conditions, what kind of testing is available, and your chances of having a baby with a genetic condition. To find a genetic counselor in your area, talk to your health care provider or contact the National Society of Genetic Counselors.

How can you find out if your baby is at risk for a genetic condition?

Your baby may be at increased risk of having a genetic condition if:

  • You or your partner has a genetic condition.
  • You have a child with a genetic condition.
  • A genetic condition runs in you or your partner’s family or ethnic group. An ethnic group is a group of people, often from the same country, who share language or culture. Certain genetic conditions, like sickle cell disease and Tay-Sachs disease, are more common in people from certain ethnic groups. For example, people who are Ashkenazi Jews are more likely than others to have Tay-Sachs and other genetic conditions. 

Your provider and genetic counselor use your family health history to learn more about genes, chromosomes and things in your life that may affect your health and your baby’s health. A family health history is a record of any health conditions and treatments that you, your partner and everyone in your families have had. Use our family health history form and share it with your provider. 

What tests can you get before pregnancy to help you find out about genetic conditions that may affect your baby?

Before pregnancy, you can have carrier screening tests that check your blood or saliva to see if you’re a carrier of certain genetic conditions. If you’re a carrier, you don’t have the condition yourself, but you have a gene change for it that you can pass to your baby. 

If both you and your partner are carriers of the same condition, the risk that your baby has the condition increases. Getting tested before pregnancy can help you and your partner look at your baby’s risk and make decisions about getting pregnant. Your partner can get tested, too. Carrier screening is your choice. You don’t have to have it if you don’t want it, even if your provider recommends it.

All women who are thinking about getting pregnant can get screened for:

  • Cystic fibrosis (also called CF). CF is a condition that affects breathing and digestion. Digestion is the way your body processes the food you eat.
  • Spinal muscular atrophy (also called SMA). SMA is a disease that attacks nerve cells in the spinal cord. It weakens muscles and can affect crawling, walking, breathing, swallowing, and head and neck control.
  • Thalassemias. These are blood conditions that cause the body to make fewer healthy red blood cells and less hemoglobin than normal. Hemoglobin is a protein in red blood cells. 
  • Hemoglobinopathies. These conditions affect red blood cells in the body.

Some women get carrier screening for certain conditions that run in families or ethnic groups. An ethnic group is a group of people, often from the same country, who share language or culture. Your provider recommends carrier screening for conditions based on your family history or ethnic group, including: 

  • Fragile X syndrome. This condition happens when the body can’t make enough of a protein it needs for the brain to grow and develop. If Fragile X syndrome runs in your family, your provider may recommend carrier testing.
  • Tay-Sachs disease. This is a condition that causes nerve cells in the brain and spine to die. It’s more common in people who are Central and Eastern European Jewish (also called Ashkenazi Jews), French-Canadian, Louisiana Cajun or Old Order Amish of Pennsylvania.

If you or your partner is a carrier (you’ve been tested to find out) and you’re having fertility treatment called in vitro fertilization (also called IVF), you may be interested in a test called preimplantation testing (also called preimplantation genetic diagnosis or PGD). In IVF, an egg and sperm are combined in a lab to create an embryo (fertilized egg) which is then implanted (put) into your uterus. This test checks cells from the embryo for gene changes before they’re implanted in your uterus. Only healthy embryos (without a gene change) are implanted. Your provider or genetic counselor can help you understand your test results and the chances of passing a genetic condition to your baby. 

After any testing, you and your partner talk with your provider and genetic counselor to understand results and how they may affect you, your baby and your family. Knowing whether or not your baby is at risk for a birth defect can help you make decisions about your baby’s future and make plans to care for and get treatment for your baby after birth.

What tests can you get during pregnancy to find out about genetic conditions that may affect your baby?

Tests you may want during pregnancy include:

  • Screening tests, including cell-free fetal DNA testing, first-trimester screening and maternal blood screening (also called a quad screen). These tests tell you if your baby is at risk for certain genetic conditions. You can have these tests as part of your prenatal tests in the first or second trimester of pregnancy. The American College of Obstetricians and Gynecologists recommends that health care providers offer all pregnant women screening tests for chromosomal conditions, including Down syndrome. Depending on the test results, your provider may recommend diagnostic tests to see for sure if your baby has a genetic condition.
  • Diagnostic tests, including amniocentesis (also called amnio) and chorionic villus sampling (also called CVS). If a screening test shows that your baby may be at risk for a condition, your provider gives you a diagnostic test, like amnio or CVS, to find out for sure. Your provider also can check your baby’s blood for certain genetic conditions after he’s born.

Again, after any testing, you and your partner can talk with your provider and genetic counselor about how test results may affect you, your baby and your family.

What are the benefits and risks of testing?

Benefits of testing are learning and knowing about your baby’s condition:

  • You may learn that your baby isn’t at risk for or doesn’t have a genetic condition.
  • If you find out your baby may have a condition, you can learn about ways to prevent the condition or find out about more testing.
  • If you find out your baby does have a condition, you can make decisions about his care. You may want to give birth in a hospital that has the best providers and equipment to treat and care for your baby. And you can find out about treatment and services available after you take your baby home.

Risks of testing include:

  • Testing may affect your feelings. You may feel angry, sad or nervous about test results.
  • Testing may affect family members. You may find out about a health condition that runs in your family, and not everyone in your family may want to know about or talk about the condition. Not everyone in your family may want to share health information.
  • Testing may not tell you everything you need to know about your baby’s condition. For example, it may not tell you how severe a condition is or if it may get worse over time. Or the test may be inconclusive. This means it doesn’t give enough information about your baby’s condition. If results are inconclusive, you may want or need more testing. 
  • Even if you know about your baby’s condition, there may be no treatment or limited treatment for it. 

Physical risks of testing are small. Many tests use just a blood or saliva sample. Tests like amnio and CVS do have a small risk of miscarriage because they take a sample of fluid or tissue from around the baby.

What problems can genetic conditions cause during and after pregnancy?

Sometimes genetic conditions can cause miscarriage or stillbirth. Miscarriage is when a baby dies in the womb before 20 weeks of pregnancy. More than half of miscarriages are caused by chromosomal conditions. Stillbirth is when a baby dies in the womb before birth but after 20 weeks of pregnancy. 

Each child born with a genetic condition is different. Problems depend on which chromosomes are affected. Some children don’t have serious problems. Some may have intellectual disabilities or birth defects or both. Intellectual disabilities are problems with how the brain works that can cause a person to have trouble or delays in physical development, learning, communicating, taking care of himself or getting along with others.

Do genes and chromosomes cause all health conditions and birth defects?

No. They cause some, but not all. We don’t know all the causes, but any of these things before or during pregnancy can make your baby more likely to be born with health conditions or birth defects: 

More information

Last reviewed: May, 2017