Prenatal Screenings & Diagnostics
Prenatal screening tests are not the same as fetal diagnostics. Prenatal screening tests are routine tests performed during pregnancy that screen for birth defects, chromosome abnormalities or other health concerns. Screening tests cannot provide a specific diagnosis; they’ll only let you know if there is a high or low risk for common disorders. Fetal diagnostics are the next step following abnormal screening, as they provide an accurate diagnosis of what health problems, if any, are present.
Types of Prenatal Screening Tests
- Ultrasonography is a routine prenatal test, which can check for signs of birth defects in the internal organs and bones. It is also used to monitor the growth of the baby. As the baby grows, the small structures of the anatomy become larger. For this reason, many birth defects are not identified until the second or third trimester of pregnancy. If an abnormality is found on ultrasound, your provider may recommend diagnostic genetic testing to determine if the birth defect is isolated or the first sign of a more complex chromosome abnormality/genetic disorder.
- Nuchal translucency (NT) evaluation is an ultrasound performed between 11 and 13 weeks of pregnancy. The nuchal translucency, or NT, is a normal fluid-filled space at the back of the baby’s neck which is present during the late first trimester and early second trimester of pregnancy. Large NT measurements are associated with an increased risk for birth defects, chromosome abnormalities (like Down syndrome), genetic disorders and poor pregnancy outcomes. The NT measurement will help your provider assess the overall health of the baby during the first trimester.
- First trimester screening (FTS) calculates the risk for Down syndrome and trisomy 18 based on several factors, including: maternal age, the NT measurement and placental proteins. In this test, an ultrasound is scheduled to measure the NT and a blood sample is sent to the lab to measure the levels of certain placental proteins. FTS is considered to be standard-of-care and is typically covered by insurance. While FTS has a higher detection rate for Down syndrome than ultrasound alone, it is not as accurate as other available screening technologies. It is common for women to receive a false positive result from FTS. If an FTS result indicates a high risk, then additional testing options will be offered.
- Non-invasive prenatal testing (NIPT) is sometimes also referred to as cell-free fetal DNA screening (cff-DNA). This technology analyzes pieces of DNA present in the mother’s blood which are not inside of a cell. The DNA pieces that represent the pregnancy come from the placenta. Most forms of NIPT are designed to give a risk assessment for common chromosome abnormalities, such as Down syndrome, trisomy 18, trisomy 13 and sex chromosome abnormalities (Turner syndrome, Klinefelter syndrome, Triple X syndrome, etc.). The sex of the baby can also be identified by this test. Because this blood test analyzes DNA from the pregnancy, it is considered to be one of the most accurate screening tests. Like any screening test, NIPT can have a false positive or false negative result, even though these false results are rare. If an NIPT result indicates a high risk, then the option of diagnostic testing will be offered.
What Are Fetal Diagnostics?
Fetal diagnostics are additional tests performed when your doctor finds an abnormality during routine prenatal screenings. These tests help you and your provider know if your baby may have a birth defect or genetic disorder. Fetal diagnostics may also be offered to women with high-risk pregnancies. Your doctor may perform fetal diagnostic tests if you:
- Are 35 years or older
- Had a previous pregnancy with a birth defect
- Have a family history of a genetic disorder
- Have certain health conditions such as autoimmune disorders, diabetes, epilepsy, or high blood pressure
- Take certain medications
Types of Fetal Diagnostics
- Chorionic villus sampling (CVS) tests a small part of the placenta to identify chromosomal or genetic disorders. Your provider may perform this test through the cervix or through the abdomen. In both cases, the placental sample is sent to a lab for genetic testing. CVS is usually performed between 10 and 12 weeks of pregnancy. In some cases, your provider may recommend following up with amniocentesis for further results.
- Amniocentesis tests the amniotic fluid that protects the unborn baby throughout pregnancy. In this test, a sample of amniotic fluid is taken using a needle through the abdomen. The amniotic fluid contains cells, which the lab will use to perform genetic testing. Sometimes, the amniotic fluid is also tested for viral infections and proteins associated with certain birth defects. Amniocentesis is usually performed between 15 and 20 weeks of pregnancy.
The Benefits of Genetic Counseling
You may find it helpful to seek genetic counseling before conception or during pregnancy. A genetic counselor will offer appropriate genetic testing options for you, your partner, and/or the pregnancy based on your family history and the results from prenatal screening tests. Genetic counseling can provide support and information before or after receiving the results of your fetal diagnostic tests. UK HealthCare offers genetic counseling for women who are concerned about genetic health issues that could compromise their health or the health of their unborn child.
Request an appointment online with our Division of Genetics and Metabolism.