Genetic Testing during Pregnancy

The options available to pregnant women for genetic testing can be very confusing. This chart presents those options in a format that may help. These tests can give the parents-to-be information about whether their fetus has certain genetic disorders.

Genetic Testing during Pregnancy

The options available to pregnant women for genetic testing can be very confusing. This chart presents those options in a format that may help. These tests can give the parents-to-be information about whether their fetus has certain genetic disorders.

Genetic Testing Table

Learn what genetic tests are right for you.

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NOTE: All testing is optional.  For cost and insurance coverage please contact your insurance carrier

Two Main Types of Prenatal Genetic Tests

Two general types of prenatal tests for genetic disorders:

  1. Prenatal Screening Tests: These tests can tell you the chances that you fetus has an aneuploidy and a few additional disorders.

  2. Prenatal Diagnostic Tests: These tests can tell you whether your fetus actually has certain disorders. These test are done on cells from the fetus or placenta obtained through amniocentesis or chorionic villus sampling (CVS).

Both screening and diagnostic testing are offered to all pregnant women.

Frequently Asked Questions

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.
  • Prenatal genetic screening tests of the pregnant woman’s blood and findings fromultrasound exams can screen the fetus for aneuploidy; defects of the brain and spine called neural tube defects; and some defects of the abdomen, heart, and facial features. These tests include first-trimester screening, second-trimester screening, combined first- and second-trimester screening, and cell-free DNA 

First-trimester screening includes a test of the pregnant woman’s blood and an ultrasound exam. Both tests usually are performed together and are done between 10 weeks and 13 weeks of pregnancy:

  • The blood test measures the level of two substances.
  • The ultrasound exam, called anuchal translucency screening, measures the thickness of a space at the back of the fetus’s neck. An abnormal measurement means there is an increased risk that the fetus has Down syndrome or another type of aneuploidy. It also is linked to physical defects of the heart, abdominal wall, and skeleton.

What is second-trimester screening?

Second-trimester screening includes the following tests:

  • The “quad” or “quadruple” blood test measures the levels of four different substances in your blood. The quad test screens for Down syndrome,trisomy 18, and neural tube defects. It is done between 15 weeks and 22 weeks of pregnancy.
  • An ultrasound exam done between 18 weeks and 20 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. These tests are generally done though the California Prenatal Screening Program.  https://www.cdph.ca.gov/Programs/CFH/DGDS/Pages/pns/default.aspx

Cell-free DNA is the small amount of DNA that is released from the placenta into a pregnant woman’s bloodstream. The cell-free DNA in a sample of a woman’s blood can be screened for Down syndrome, trisomy 13, trisomy 18, and problems with the number of sex chromosomes. This test can be done starting at 10 weeks of pregnancy. It takes about 1 week to get the results. A positive cell-free DNA test result should be followed by a diagnostic test with amniocentesis or CVS. 

The cell-free DNA screening test works best for women who already have an increased risk of having a baby with a chromosome disorder. For a woman at low risk of having a baby with a chromosome disorder, conventional screening remains the most appropriate choice. We most often recommend  Panorama for those wanting to do cell-free DNA testing. https://www.natera.com/panorama-test/common-questions

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. A screening test result that shows there is not a problem when one does exist is called a false-negative result. Your health care professional can give you information about the rates of false-positive and false-negative results for each test. 

Amniocentesis is a diagnostic test. It usually is done between 15 weeks and 20 weeks of pregnancy, but it also can be done up until you give birth. To perform the test, a very thin needle is used to withdraw a small amount of amniotic fluidUltrasound is used to guide the procedure. Depending on the way the cells are analyzed and the information that you want, results can take from 1 day to several weeks. There is a very small chance of pregnancy loss with amniocentesis. Leakage of amniotic fluid and slight bleeding can occur after amniocentesis. In most cases, both stop on their own.

CVS is another type of diagnostic test. In CVS, a sample of tissue is taken from the placenta. The two main advantages of having CVS over amniocentesis are that 1) CVS is performed earlier than amniocentesis, between 10 weeks and 13 weeks of pregnancy, and 2) the results are usually ready sooner for standard testing. With an experienced doctor, CVS carries about the same risk of pregnancy loss as amniocentesis.

Most of the time, the results of a diagnostic test are negative (normal). A negative result does not rule out the possibility that the fetus has a genetic disorder. It only tells you that the fetus does not have the particular disorder that was tested for.

If a diagnostic test result is positive (it shows that the fetus has the disorder tested for), your obstetrician or genetic counselor can explain the results and provide guidance about your choices and options. A specialist in the disorder can help you understand the life expectancy of the disorder, whether treatment is available, and the care that your child will need. Support groups, counselors, and social workers also can listen to your concerns and answer questions. It may be possible to have additional testing, such as a specialized ultrasound exam, to find out more detail about the defect.

It is your choice whether to have prenatal testing. Your personal beliefs and values are important factors in the decision about prenatal testing.

It can be helpful to think about what you would do if a diagnostic test result comes back positive. Some parents want to know beforehand if their child will be born with a genetic disorder. This gives parents time to learn about the disorder and plan for medical care that the child may need. If the disorder is very serious and the life expectancy is short, hospice care for the baby can be planned. Some parents may decide to end the pregnancy in certain situations. Other parents do not want to know this information before the child is born. They may decide not to have any testing at all. There is no right or wrong answer.

Keep in mind that certain tests can be done only at certain times during pregnancy. Tests that are done earlier allow parents more time to make decisions if a test result is positive. If ending the pregnancy is being considered, it is safer to do so within the first 13 weeks of pregnancy.

Any woman can choose to have diagnostic testing instead of or in addition to screening. The main benefit of having diagnostic testing instead of screening is that it can detect all conditions caused by an extra chromosome and many other disorders in which chromosomes are missing or damaged. Diagnostic tests also are available for many inherited disorders. The main disadvantage is that diagnostic testing carries a very small risk of losing the pregnancy. A genetic counselor or other health care professional with expertise in genetics can study your family health history, recommend specific tests, and interpret test results.

It is your choice whether to have prenatal testing. Your personal beliefs and values are important factors in the decision about prenatal testing. 

It can be helpful to think about how you would use the results of prenatal screening tests in your pregnancy care. Remember that a positive screening test tells you only that you are at higher risk of having a baby with Down syndrome or another aneuploidy. A diagnostic test should be done if you want to know a more certain result. Some parents want to know beforehand that their baby will be born with a genetic disorder. This knowledge gives parents time to learn about the disorder and plan for the medical care that the child may need. Some parents may decide to end the pregnancy in certain situations.

Other parents do not want to know this information before the child is born. In this case, you may decide not to have follow-up diagnostic testing if a screening test result is positive. Or you may decide not to have any testing at all. There is no right or wrong answer.

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