Prenatal testing, including screening and diagnostic tests, can provide valuable information about your baby's health. Understand the risks and benefits.By Mayo Clinic Staff
Pregnancy is a time of great anticipation — and, sometimes, anxiety. You might worry that your baby will have health problems. While most babies are born healthy, it's important to understand your options for obtaining details about your baby's health.
The two main types of prenatal testing are:
- Screening tests. Prenatal screening tests can identify whether your baby is more or less likely to have certain birth defects, many of which are genetic disorders. These tests include blood tests, a specific type of ultrasound and prenatal cell-free DNA screening. Prenatal screening tests are usually offered during the first or second trimester. Screening tests can't make a definitive diagnosis. If results indicate an increased risk for a genetic disorder, your health care provider will discuss your options for a diagnostic test to confirm the diagnosis.
- Diagnostic tests. If a screening test indicates a possible problem — or your age, family history or medical history puts you at increased risk of having a baby with a genetic problem — you might consider an invasive prenatal diagnostic test. A diagnostic test is the only way to be sure of a diagnosis. Some diagnostic tests, such as chorionic villus sampling and amniocentesis, carry a slight risk of miscarriage.
Prenatal screening tests include:
- First trimester screening tests. During your first trimester, your health care provider will offer a blood test and an ultrasound to measure the size of the clear space in the tissue at the back of a baby's neck (nuchal translucency). In Down syndrome and in certain other conditions, the nuchal translucency measurement is abnormally large.
- Second trimester screening tests. During your second trimester, your health care provider will offer another blood test called the quad screen. This test measures levels of four substances in your blood. Results indicate your risk of carrying a baby who has certain chromosomal conditions, such as Down syndrome. The test can also help detect neural tube defects — serious abnormalities of the brain or spinal cord.
- Prenatal cell-free DNA screening. This blood test examines fetal DNA in the maternal bloodstream to screen for the increased chance for specific chromosome problems, such as Down syndrome. This screening can also provide information about a baby's sex and rhesus (Rh) blood type.
Prenatal screening tests for fetal abnormalities are optional. It's important to make an informed decision about prenatal testing, especially if you're screening for fetal conditions that can't be treated. Before going forward, consider these questions:
- What will you do with the test results? Normal results can ease your anxiety. However, if prenatal testing indicates that your baby might have a birth defect, you could be faced with wrenching decisions — such as whether to continue the pregnancy. On the other hand, you might welcome the opportunity to plan for your baby's care in advance.
- Will the information shape your prenatal care? Some prenatal tests detect problems that can be treated during pregnancy. In other cases, prenatal testing alerts your health care provider to a condition that requires immediate treatment after birth.
- How accurate are the results? Prenatal screening isn't perfect. The rate of inaccurate results, known as false-negative or false-positive results, varies from test to test.
- What are the risks? Weigh the risks of specific prenatal tests — such as anxiety, pain or possible miscarriage — against the value of knowing the results.
The decision to pursue prenatal testing is up to you. If you're concerned about prenatal testing, discuss the risks and benefits with your health care provider. You might also meet with a genetic counselor for help choosing a test and understanding the results.
Taking the time to evaluate your options will help you make the best decision for you and your baby.
Sept. 12, 2018
- American College of Obstetricians and Gynecologists Committee on Genetics. Committee Opinion No. 693: Counseling about genetic testing and communication of genetic test results. Obstetrics & Gynecology. 2017;129:96.
- American College of Obstetricians and Gynecologists (ACOG) Committee on Practice Bulletins — Obstetrics, Committee on Genetics, and the Society for Maternal-Fetal Medicine. ACOG Practice Bulletin No. 162: Prenatal diagnostic testing for genetic disorders. Obstetrics & Gynecology. 2016;127:108.
- American College of Obstetricians and Gynecologists (ACOG) Committee on Practice Bulletins — Obstetrics, Committee on Genetics, and the Society for Maternal-Fetal Medicine. ACOG Practice Bulletin No. 163: Screening for fetal aneuploidy. Obstetrics & Gynecology. 2016;127:979.
- Frequently asked questions. Pregnancy FAQ165. Prenatal genetic screening tests. American College of Obstetricians and Gynecologists. https://www.acog.org/Patients/FAQs/Prenatal-Genetic-Screening-Tests. Accessed Aug. 20, 2018.