Modern genetics allows us to understand how genetic diseases are inherited based on DNA, genes, and chromosomes. We can now test couples and fetuses for certain inherited disorders, such as cystic fibrosis, as well as other chromosomal and genetic abnormalities, such as Down syndrome.
Couples who are thinking about having a child may consider genetic counseling and prenatal diagnosis before conception to predict any possible abnormalities in their child. Others may use the tests after they conceive to evaluate the condition of the fetus.
People who are at increased risk of passing genetic abnormalities on to their children include:
- People with family histories of inherited disorders, or those who have previously had children with genetic disorders.
- Jews of Eastern European descent, who may have a high risk of having children with Tay-Sachs or Canavan’s, metabolic disorders that lead to death in early childhood.
- African-Americans, who may risk passing on sickle-cell anemia to their children.
- Couples of Southeast Asian or Mediterranean origin, who are at increased risk of having children with thalassemia, a severe form of anemia.
- Women who were exposed to toxins that could cause birth defects.
- Women with prior medical conditions or diseases that may affect their fetus, such as diabetes.
- Couples who share a common ancestor.
- Women with a history of multiple miscarriages.
- Couples who have family members with birth defects or severe developmental problems.
Prenatal testing for genetic problems may be done before or after conception. Testing for spina bifida or Down syndrome is done after a pregnancy is established. Besides the couples listed above, counseling and diagnosis are also recommended for mothers over the age of 35, and those who have received abnormal screening test results, such as alpha-fetoprotein (AFP). For more information about the alpha-fetoprotein test, and when and why you might have it, see alpha-fetoprotein.
For those who may be at risk, genetic counseling and prenatal diagnosis are used to help answer some important questions, such as:
- Should we have a baby? Are the chances of having a baby with a genetic defect so high that choosing adoption or artificial insemination may be a better way to start a family?
- How can we treat the fetus' potential defects? Are there surgical techniques available or other medical interventions that may help alleviate problems?
- How do we prepare, physically and psychologically, for the possible outcome of a pregnancy? Are there special educational classes, training, or information that we need in order to raise a child with defects?
- Should we continue the pregnancy? Are the fetus' abnormalities so severe that we might choose to have an abortion?
It is important to remember that preconception testing can only give you the odds of having a child with a certain birth defect; a genetic counselor maps out the specific numbers. You may learn, for example, that you have a one in four chance of having a child with a certain disorder. If you decide to conceive, the fetus may be able to undergo prenatal testing to show whether or not the baby has inherited the disorder.
How Can I Prepare?
You may wish to discuss genetic counseling with your family, as well as your health care provider, who may refer you to a genetic counselor specially trained to understand the complex issues surrounding heredity and pregnancy. Find out if any medical problems run in your family, especially any problems with child development, miscarriages, stillbirths, or severe childhood illnesses. If you decide to get the blood-screening test, make sure your health care provider talks to you beforehand and answers any of your questions.
What Will Happen?
You will be required to fill out an in-depth family history, and discuss your family's medical past with the counselor. You and your partner may also take simple blood tests, or undergo an analysis of your chromosomes known as karyotyping. All this information will be considered together to help determine what genetic patterns you may pass on to your children. If you choose to be tested after conception, one of the following tests will be used to obtain fetal cells whose genetic and chemical makeup can be analyzed in a laboratory:
- Amniocentesis, in which fluid is withdrawn from the amniotic sac and analyzed. See amniocentesis for more information.
- Chorionic villus sampling (CVS), which takes a sampling of the cells of the placenta. See CVS for more information.
- Percutaneous umbilical blood sampling (PUBS), which draws fetal blood from the umbilical cord. See PUBS for more information.
What Are The Risks?
The tests used for genetic counseling have virtually no risks. The tests used after conception, however, may cause infection, damage to the fetus, or miscarriage. For further information, see the articles on amniocentesis, CVS, and PUBS.
Frequently Asked Questions
Q: If I am in a risk group, do I have to get tested?
A: No. It is up to you whether or not to undergo genetic counseling and prenatal testing. Your religious or philosophical beliefs, family circumstances, and personal desires all are a part of the decision-making process.
Q: If I discover I am a carrier of a certain disease, will I still be allowed to have a baby?
A: Absolutely. The point of genetic counseling and prenatal diagnosis is simply to provide parents with information that they need to make important decisions. A good genetic counselor will help you figure out how to use the information you discover, but will not make any decisions for you. If you are at risk of having a baby with a disorder, you may be able to use assisted reproductive technologies to reduce the chance that your baby will be affected.
Reviewed By: Irina Burd, MD, PhD, Maternal Fetal Medicine, Johns Hopkins University, Baltimore, MD. Review provided by VeriMed Healthcare Network.