Results for prenatal testing are usually available more quickly because time is an important consideration in making decisions about a pregnancy. The doctor or genetic counselor who orders a particular test can provide specific information about the cost and time frame associated with that test. Other chapters in Help Me Understand Genetics. Genetics Home Reference has merged with MedlinePlus.
Learn more. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. During pregnancy, ultrasound can be used to check the fetus. Copyright by the American College of Obstetricians and Gynecologists. All rights reserved.
Read copyright and permissions information. This information is designed as an educational aid for the public. It offers current information and opinions related to women's health. It is not intended as a statement of the standard of care. It does not explain all of the proper treatments or methods of care. It is not a substitute for the advice of a physician. There are two types of prenatal tests for genetic disorders: Prenatal screening tests : These tests can tell you the chances that your fetus has an aneuploidy and a few other disorders.
Both screening and diagnostic testing are offered to all pregnant women. They include carrier screening and prenatal genetic screening tests: Carrier screening is done on parents or those just thinking about becoming parents using a blood sample or tissue sample swabbed from inside the cheek. Both tests usually are done together between 10 weeks and 13 weeks of pregnancy: The blood test measures the level of two substances. Results of blood screening tests for aneuploidy are reported as the level of risk that the disorder might be present: A positive screening test result for aneuploidy means that your fetus is at higher risk of having the disorder compared with the general population.
Diagnostic Tests: Tests that look for a disease or cause of a disease. Genetic Disorders : Disorders caused by a change in genes or chromosomes. Monosomy: A condition in which there is a missing chromosome. Mutations: Changes in genes that can be passed from parent to child.
Obstetrician: A doctor who cares for women during pregnancy and their labor. Trimester: A 3-month time in pregnancy. It can be first, second, or third.
Trisomy: A condition in which there is an extra chromosome. Article continues below Advertisement. If you have further questions, contact your ob-gyn. Don't have an ob-gyn? Search for doctors near you. Learn About the Book. Find an Ob-Gyn Search for doctors near you. But in most cases — including cystic fibrosis and sickle cell disease — a child has to inherit one altered gene from each parent.
Ideally, parents will be tested for some genetic disorders before they conceive, but they can also be tested during pregnancy. In almost all cases, testing is recommended for one parent.
Testing the second parent only becomes necessary if the first tests positive. In the past, the American College of Obstetricians and Gynecologists ACOG only recommended carrier screenings to parents of certain ethnic or geographic backgrounds considered more at risk of specific disorders. However, some conditions are not limited to one ethnicity. The group now recommends that all women should get screened for cystic fibrosis and spinal muscular atrophy SMA as well as some inheritable blood disorders, including sickle cell disease and thalassemias.
Because some people are more likely to carry specific genetic mutations than others, your doctor may recommend a number of other screenings based on your family heritage or medical history:. Expanded carrier screening enables all couples, regardless of their ethnic or geographical profile, to test for a broad array of genetic conditions before conceiving.
It can screen for the carrier gene of hundreds of diseases, giving you the power of knowing whether you and your partner are at risk of passing along any of these genetic conditions to a baby you conceive together. That said, just because the test is available does not mean couples should be screened for all the diseases out there. ACOG has specific recommendations for which disorders practitioners should include in an expanded carrier panel.
These include conditions that occur in at least 1 in people, reduce the quality of life, impair cognitive or physical abilities, require surgical or medical intervention and have an onset in childhood. Carrier screenings test for genetic diseases that have a carrier frequency of at least 1 in — meaning that the mutation is present in at least 1 in every people. Here are a few of the most common genetic diseases that an expanded carrier screening can test for:. Alpha thalassemia is a blood disorder that causes a reduction in the amount of hemoglobin, a protein in the red blood cells that carries oxygen throughout the body.
This can lead to weakness, anemia and other problems. Beta thalassemia is another blood disease that causes a reduction in the amount of hemoglobin in the body. It can lead to anemia, fatigue, blood clots and other complications. This condition causes lung infections and difficulty breathing.
In people with cystic fibrosis, thick, excess mucus clogs the airways and traps bacteria, which can cause infections and other complications. Familial hyperinsulinism is characterized by high levels of the hormone insulin.
People with familial or congenital hyperinsulinism can have low blood sugar, plus more serious complications like seizures and breathing trouble.
This is a bone marrow disorder that causes a reduction in the number of blood cells in the body. Chorionic villus sampling CVS usually is done between weeks 10 and 12 of pregnancy. The doctor removes a small piece of the placenta to check for genetic problems in the fetus. Because chorionic villus sampling is an invasive test, there's a small risk that it can induce a miscarriage. A doctor may recommend genetic counseling or testing for any of these reasons: The pregnant woman is over age A pregnant woman's chances of having a child with a chromosomal problem such as trisomy increase if she is older than Children of older fathers are at risk for new dominant genetic mutations — those caused by a single genetic defect that hasn't run in the family before.
A standard prenatal screening test had an abnormal result. Doctors may recommend genetic testing if a screening test showed a possible genetic problem. A couple plans to start a family and one of them or a close relative has an inherited illness. Some people are carriers of genes for genetic illnesses, even though they don't show signs of the illness themselves. This happens because some genetic illnesses are recessive. This means they cause symptoms only if a person inherits two copies of the problem gene, one from each parent.
Children who inherit one problem gene from one parent but a normal gene from the other parent won't have symptoms of a recessive illness. A parent already has one child with a serious birth defect. Not all children who have birth defects have genetic problems.
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