Genetic and chromosomal conditions

What are genes and chromosomes?

Genes are part of your body’s cells that store instructions for the way your body grows and works. Genes are passed from parents to children. Each person has more than 20,000 genes. 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.

Sometimes the instructions that are stored in a gene change. This is called a gene change or a mutation. A gene can change on its own, or it can be passed from parents to children.

A gene change can sometimes cause health conditions, like cystic fibrosis and sickle cell disease. A gene change also can cause birth defects, like heart defects. Birth defects are structural changes present at birth that can affect almost any part of the body. They may affect how the body looks, works or both. Birth defects can cause problems in overall health, how the body develops or how the body works.

Any condition caused by a gene change is called a genetic condition (also called a genetic disorder). Some types of genetic conditions are caused by problems in one or more chromosomes. Chromosomes are the structures 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 (also called chromosomal disorders) in a baby. One of the most common chromosomal conditions is Down syndrome (when there are three copies of chromosome 21 instead of two). Parents can pass chromosome changes to their children, or they can happen on their own as cells develop.

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 is a person who is trained to help you understand about genes, birth defects and other medical conditions that run in families, and how they can affect your health and your baby’s health. A genetic counselor 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 your 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.

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?

Carrier screening. Before pregnancy, you can have carrier screening tests that check your blood, saliva or tissue from inside your cheek 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.

Your partner can get tested, too. 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. 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 carrier screening for:

• Cystic fibrosis (also called CF). CF is a condition that affects breathing and digestion. Digestion is the process of how your body breaks down food after you eat.
• Spinal muscular atrophy (also called SMA). SMA is a group of conditions that causes muscle damage and weakness. It eventually leads to death.
• Hemoglobinopathies. These conditions affect red blood cells in the body. Types of hemogloinopathies include:
  • 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.
  • Sickle cell disease. This is a blood condition that causes red blood cells to be shaped like a “C.”

Targeted carrier screening. Some women get carrier screening for certain conditions that run in families or ethnic groups. This is called targeted carrier screening or ethnic-based carrier screening. Your provider may recommend targeted carrier screening for conditions based on your family history or ethnic group, including:

• Fragile X syndrome (also called FXS). 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 for this genetic condition.
• 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 Eastern and Central European Jewish (also called Ashkenazi Jews), French-Canadian, Louisiana Cajun or Old Order Amish of Pennsylvania.

Preimplantation genetic testing. If testing shows that you or your partner is a carrier of a genetic condition and you’re having fertility treatment called in vitro fertilization (also called IVF), another testing option is preimplantation genetic testing (also called preimplantation genetic diagnosis). IVF is when an egg and sperm are combined in a lab to create an embryo (fertilized egg) which is then put in your uterus. This test checks cells from the embryo for gene changes before they’re put in your uterus. Your IVF provider can then choose embryos that don’t test positive for a gene change. 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 genetic condition 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 can get during pregnancy include:

• Screening tests, including first-trimester screening, maternal blood screening (also called a quad screen) and cell-free DNA testing. These tests have some limitations. They tell you if your baby may be at risk for certain genetic conditions. But they do not tell you if your baby definitely has a condition. Sometimes these tests can have incorrect results. You can have screening tests as part of your prenatal tests in the first or second trimester of pregnancy.
• Diagnostic tests, including amniocentesis (also called amnio) and chorionic villus sampling (also called CVS). A diagnostic test is a test to see if you or your baby has or doesn’t have a health condition. If a screening test shows that your baby may be at risk for a condition, you can get a diagnostic test, like amnio or CVS, to find out for sure. The decision is up to you. Your provider also can check your baby’s blood for certain genetic conditions after he’s born.

The American College of Obstetricians and Gynecologists (ACOG) recommends that health care providers offer all pregnant women prenatal screening and diagnostic tests. ACOG recommends that providers give clear information about these tests so that you can make a decision that’s right for you. Before and after any testing, you and your partner can talk with your provider, a genetic counselor or both 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 include:

• You may learn that your baby isn’t at risk for or doesn’t have the genetic conditions you tested for.
• If you find out your baby may be at higher risk for a condition, you can find out about more testing.
• If you find out your baby does have a condition, you can find out if treatment is available during pregnancy or right after birth and 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. You can find out about support services available for you and your partner. And you can learn 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 need to decide whether to get 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. Diagnostic tests like amnio and CVS 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 after 20 weeks of pregnancy. Sometimes babies with certain genetic conditions do not survive long after birth.

Each child born with a genetic condition is different. Problems depend on which genes or chromosomes are affected. Some children don’t have serious problems. Some may have birth defects or intellectual and developmental disabilities or both. Intellectual and developmental 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 these things may increase the risk of your baby being born with a health condition or birth defect:

• Smoking, drinking alcohol or taking street drugs during pregnancy
• Taking certain medicines before or during pregnancy
• Getting certain infections during pregnancy
• Having certain health conditions that are not managed well
• Being in contact with harmful chemicals

More information

Centers for Disease Control and Prevention (CDC)

CDC Show Your Love Campaign

Einstein Victor Center for the Prevention of Jewish Genetic Diseases

Genetic Alliance

JScreen at Emory University

National Center for Education on Maternal and Child Health

National Organization for Rare Disorders (NORD)

National Society of Genetic Counselors

Last reviewed: April, 2022