Genetic Screening before or during Pregnancy

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KEY POINTS

• Genetic screening is a way to check for birth defects or illnesses that might be passed from parents to children.
• You will asked about diseases, disorders, and birth defects in your families. Both you and your partner may have blood tests. You may also have an ultrasound, which uses sound waves to show pictures of your uterus, the baby, and the tissue and fluid that surrounds and protects your baby.
• Your healthcare provider or counselor will discuss the screening results with you.

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What is genetic screening?

Genes are in each cell of your body. They contain the information that tells your body how to develop and work. Changes in the genes can be passed from parents to children. If you are planning to have a baby, you may be concerned about birth defects or illnesses that your child might inherit. Genetic screening is a way to learn more about this. You can have the screening before or during pregnancy.

When is it used?

All women should be offered genetic screening during pregnancy. You should have a chance to ask questions about the different kinds of tests and to get counseling if you would like it. You can choose not to have genetic screening and still receive complete pregnancy care. Genetic screening is recommended if:

• The mother will be 35 years old or older at the time of delivery, which increases the risk that your baby will have birth defects
• You have already had a child with an inherited disease or birth defect
• You have had stillbirths or several miscarriages. (Stillbirth is death of the baby before it is born, after 20 weeks of pregnancy.)
• You had diabetes before you became pregnant.
• Something about the pregnancy is not normal. For example, blood test results have been abnormal. Or there is too much or not enough fluid around the baby.
• Someone in your family has had:
  • Intellectual disability or other developmental problems
  • Hemophilia, which is a blood clotting problem
  • Cystic fibrosis, which is a disease that causes the body to make thick, sticky mucus
  • Sickle cell anemia, which causes abnormally shaped red blood cells
  • Thalassemia, which causes abnormal red blood cells that don’t last as long as normal red blood cells
  • Tay-Sachs disease, which causes fatty proteins to build up and cause nerve damage and can cause early death

How do I prepare for genetic screening?

Learn the medical history of members of your family. Try to get details of any inherited diseases in your family. Ask your parents and grandparents if they know of children in the family who had birth defects, or learning or development problems.

Be ready to give the following information about yourself:

• Past miscarriages
• Exposure to chemicals, radiation (including X-rays), or other environmental hazards before or during pregnancy
• Any history of drug or alcohol abuse
• Prescription, nonprescription, and herbal medicines taken during pregnancy, including before you knew you were pregnant

How is genetic screening done?

The first step in genetic screening is for you and the baby’s father to answer questions about yourselves and your families’ health. Your healthcare provider or genetic counselor will review your family and personal medical histories. You will be asked about diseases, disorders, and birth defects in your families. Both you and your partner may have blood tests. Tests of the baby may also be done while you are pregnant.

Common tests used to screen for genetic conditions in pregnancy include:

• Blood tests
• An ultrasound, which uses sound waves to show pictures of your uterus, the baby, and the tissue and fluid that surrounds and protects your baby. Ultrasound can find genetic problems that are not found with routine blood tests.

No single test or mix of tests can find all forms of birth defects or genetic problems. Most screening tests give information about the chances of a problem. They do not give a yes or no answer about whether there actually is a problem. Depending on information you give to your healthcare provider or your screening test results, other tests may be done. These tests are more than screening tests. They can diagnose certain conditions. These tests include:

• Chorionic villus sampling (CVS), which takes a small sample of tissue from the placenta (the tissue that carries oxygen and food from your blood to the baby’s blood.) This test is usually done between the 10th and 13th weeks of pregnancy.
• Amniocentesis, which uses a needle put through your belly to test the fluid that surrounds your baby. This test is usually done between the 15th and 18th weeks of pregnancy.
• Tests of DNA in a sample of tissue from the baby. The sample of tissue may be done when you have amniocentesis.
• Testing of blood from the umbilical cord

Your healthcare provider or counselor will discuss the screening results with you. If there is a problem, they will help you to understand the problem. They will describe your choices for prevention or treatment.

For more information, contact:

• The Genetic Alliance
  800-336-4363
  http://www.geneticalliance.org
• The March of Dimes
  888-663-4637
  http://www.marchofdimes.org/