When is genetic screening done

June 13, AM. Pregnancy screening options Women choose to undergo or decline screening for a variety of reasons. Diagnostic testing in pregnancy Diagnostic tests provide more accuracy as well as information about conditions not included in screening. How genetic testing affects parents The majority of patients who choose to have prenatal genetic testing do so for a simple reason: knowledge.

Genetic Counseling. Prenatal Genetic Testing. Pregnancy Complications. Heart Health. Health Management. From Genetics Home Reference. Topics in the Genetic Testing chapter What is genetic testing? What are the different types of genetic tests? What are the uses of genetic testing?

What is informed consent? How can I be sure a genetic test is valid and useful? What do the results of genetic tests mean? What is the cost of genetic testing, and how long does it take to get the results? Will health insurance cover the costs of genetic testing? Genetic tests are when small samples of blood or body tissues are analyzed.

Many different types of body fluids and tissues can be used. The type of genetic test needed to make a diagnosis depends on which condition a doctor checks for.

For genetic testing before birth, a blood test can screen pregnant women for some disorders. To check for others, or if the screening blood test finds a possible problem, doctors may recommend amniocentesis or chorionic villus sampling:.

Progress in genetic testing has improved how doctors diagnose and treat some illnesses. But it has limits. Genetic tests can identify a particular problem gene. But they can't always determine how that gene will affect the person who carries it. In cystic fibrosis , for example, finding a problem gene on chromosome number 7 can't predict whether a child will have serious lung problems or milder respiratory symptoms.

Also, having problem genes is only part of the story. Many illnesses develop from a mix of high-risk genes and environmental things, some of which a person can control. Someone who knows they carry high-risk genes might be able to make lifestyle changes to avoid becoming sick.

Research has identified genes that put people at risk for cancer, heart disease, psychiatric disorders, and many other medical problems. The hope is to someday develop specific types of gene therapy to prevent some diseases and illnesses. This FAQ focuses on these tests. Prenatal diagnostic tests : These tests can tell you whether your fetus actually has certain disorders. These tests are done on cells from the fetus or placenta obtained through amniocentesis or chorionic villis sampling CVS.

Screening tests can tell you your risk of having a baby with certain disorders. 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.

These tests are used to find out whether a person carries a gene for certain inherited disorders. Carrier screening can be done before or during pregnancy. They include first- trimester screening, second-trimester screening, combined first- and second-trimester screening, and cell-free DNA testing. Both tests usually are done together between 10 weeks and 13 weeks of pregnancy:. An abnormal measurement means there is an increased risk that the fetus has Down syndrome trisomy 21 or another type of aneuploidy.

It also is linked to physical defects of the heart, abdominal wall, and skeleton. It is done between 15 weeks and 22 weeks of pregnancy. An ultrasound exam done between 18 weeks and 22 weeks of pregnancy checks for major physical defects in the brain and spine, facial features, abdomen, heart, and limbs.

The results from first-and second-trimester tests can be combined in various ways. Combined test results are more accurate than a single test result. If you choose combined screening, keep in mind that final results often are not available until the second trimester. This test can be done starting at 10 weeks of pregnancy.

It takes about 1 week to get the results. 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. It does not mean that your fetus definitely has the disorder.

A negative result means that your fetus is at lower risk of having the disorder compared with the general population. It does not rule out the possibility that your fetus has the disorder. Diagnostic testing with CVS or amniocentesis that gives a more definite result is an option for all pregnant women.

Your obstetrician or other health care professional, such as a genetic counselor , will discuss what your screening test results mean and help you decide the next steps. With any type of testing, there is a possibility of false-positive results and false-negative results. A screening test result that shows there is a problem when one does not exist is called a false-positive result.