Prenatal genetic counseling
Genetics is the study of heredity, the process of a parent passing certain genes on to their children.
- A person's appearance, such as height, hair color, skin color, and eye color, are determined by genes.
- Birth defects and certain diseases are also often determined by genes.
What is Prenatal Genetic Counseling?
Prenatal genetic counseling is the process where parents can learn more about:
- How likely it will be that their child would have a genetic disorder
- What tests can check for genetic defects or disorders
- Deciding whether or not you would like to haven these tests
Couples who want to have a baby can have tests before they get pregnant. Health care providers can also test a fetus (unborn baby) to see if the baby will have a genetic disorder, such as cystic fibrosis or Down syndrome.
Who may Want Prenatal Genetic Counseling?
It is up to you whether or not to have prenatal genetic counseling and testing. You will want to think about your personal desires, religious beliefs, and family circumstances.
Some people have a greater risk than others for passing on genetic disorders to their children. They are:
- People who have family members or children with genetic or birth defects.
- Jews of Eastern European descent. They may have a high risk of having babies with Tay-Sachs or Canavan's disease.
- African-Americans, who may risk passing sickle-cell anemia (blood disease) on to their children.
- People of Southeast Asian or Mediterranean origin, who are at a higher risk of having children with thalassemia, a blood disease.
- Women who were exposed to toxins (poisons) that could cause birth defects.
- Women with a health problem, such as diabetes, that may affect their fetus.
- Couples who have had three of more miscarriages (fetus dies before 20 weeks of pregnancy).
Testing is also suggested for:
- Women who are over the age of 35, though genetic screening is now recommended for women of all ages.
- Women who have had abnormal results on pregnancy screening, such as alpha-fetoprotein (AFP).
- Women whose fetus shows abnormal results on pregnancy ultrasound.
Talk about genetic counseling with your provider and your family. Ask questions you may have about the test and what the results will mean for you.
What Will Counseling and Tests Tell me?
Keep in mind that genetic tests that are done before you get pregnant (conceive) can most often only tell you the odds of having a child with a certain birth defect. For instance, you may learn that you and your partner have a 1 in 4 chance of having a child with a certain disease or defect.
If you decide to conceive, you will need more tests to see if your baby will have the defect or not.
For those who may be at risk, test results can help answer such questions as:
- Are the chances of having a baby with a genetic defect so high that we should look at other ways to start a family?
- If you have a baby with a genetic disorder, are there treatments or surgeries that can help the baby?
- How do we prepare ourselves for the chance we might have a child with a genetic problem? Are there classes or support groups for the disorder? Are there providers nearby who treat children with the disorder?
- Should we continue the pregnancy? Are the baby's problems so severe that we might choose to end the pregnancy?
What Will Happen?
You can prepare by finding out if any medical problems like these run in your family:
- Child development problems
- Severe childhood illnesses
Steps in prenatal genetic counseling include:
- You will fill out an in-depth family history form and talk to the counselor about health problems that run in your family.
- You may also get blood tests to look at your chromosomes or other genes.
- Your family history and test results will help the counselor look at genetic defects you may pass on to your children.
If you choose to be tested after you become pregnant, tests that may be done during the pregnancy (either on the mother or fetus) include:
- Amniocentesis, in which fluid is withdrawn from the amniotic sac (fluid that surrounds the baby).
- Chorionic villus sampling (CVS), which takes a sample of the cells from the placenta.
- Percutaneous umbilical blood sampling (PUBS), which tests blood from the umbilical cord (the cord that connects the mother to the baby).
- Noninvasive prenatal screening, which looks in the mother's blood for DNA from the baby that may have an extra or missing chromosome.
These tests have some risks. They may cause infection, harm the fetus, or cause a miscarriage. If you are worried about these risks, talk to your provider.
What if I Carry a Genetic Disorder?
The purpose of prenatal genetic counseling is simply to help parents make informed decisions. A genetic counselor will help you figure out how to use the information you get from your tests. If you are at risk, or if you find out that your baby has a disorder, your counselor and provider will talk to you about options and resources. But the decisions are yours to make.
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Nussbaum RL, McInnes RR, Willard HF. Prenatal diagnosis and screening. In: Nussbaum RL, McInnes RR, Willard HF, eds. Thompson & Thompson Genetics in Medicine. 8th ed. Philadelphia, PA: Elsevier; 2016:chap 17.
Wapner RJ. Prenatal diagnosis and congenital disorders. In: Creasy RK, Resnick R, Iams JD, Lockwood CJ, Moore TR, Greene MF, eds. Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice. 7th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 30.