Common Tests Used During Pregnancy
Beginning with your first prenatal visit to your doctor, you may be asked to undergo various tests to monitor your health and the health of your developing baby. Some of these tests are capable of detecting genetic or developmental problems in the fetus. Such tests can provide warning that your developing baby will be born with special needs.
The following are some of the tests that are commonly performed during pregnancy.
- Triple Screen Test (or Triple Marker). The Triple Screen is a blood test capable of determining whether or not your baby may be at risk for birth defects, such as Spina Bifida, or chromosomal abnormalities, such as Down Syndrome (a common form of mental retardation). The test works by measuring levels of Alpha Fetoprotein (AFP), Human Chorionic Gonadotrophin (HCG), and Estriol in the blood. It is generally performed between the 16th and 18th weeks of pregnancy. Although the Triple Screen test can indicate abnormalities, it cannot diagnose actual problem with the fetus. Your doctor will recommend that additional tests be performed should the results of the Triple Screen show that your baby is at risk. For example, an ultrasound examination of your developing baby’s body (especially the baby's spine) may be indicated.
- Nuchal Translucency Screening Test. This screening test, also known as the nuchal fold scan, uses ultrasound to measure the translucency, or clear space, at the back of the developing fetus’s neck. Researchers have studied the ultrasounds of thousands of babies between the 11th and 14th weeks of gestation (the period where this test is possible) and have determined the average size of the fluid at the back of a baby’s neck each day during these three weeks. Fetuses with genetic problems, such as Down Syndrome, have more fluid at the back of the neck during this period than fetuses without such problems. Like the Triple Screen Test, this test cannot diagnoses a problem with your fetus, but instead, can help you to decide whether you want to undergo more invasive testing, such as an Amniocentesis or CVS.
- Amniocentesis. In Amniocentesis, a sample of the amniotic fluid that surrounds the fetus while it develops inside its mother is collected and analyzed so as to learn about your baby's genetic development or to check for infection. This optional test, available at 15 to 16 weeks gestation, may be performed for a variety of reasons, including advanced maternal age, previous problematic pregnancies, or a family history of genetic problems. The test involves guiding a needle through the mother’s abdomen and into her uterus with the assistance of ultrasound pictures of the inside of her abdomen. A small amount of amniotic fluid is removed and sent to the laboratory for testing. Unlike the Triple Screen, Amniocentesis can accurately diagnose nearly all chromosomal disorders, including Down Syndrome, many genetic disorders, such as Tay-Sachs disease, and neural tube defects, such as Spina Bifida. Although Amniocentesis is a routine procedure, there remains a small risk that performing the test will cause miscarriage. Your doctor can advise you as to the risks and benefits of Amniocentesis.
- Chorionic Villus Sampling (CVS). Chorionic Villus Sampling is another technique for testing the fetus' genetic development. CVS involves the removal of placental tissue. During the procedure a sample of the placenta is removed, either through the cervix (within the vagina) or through the abdomen as in an Amniocentesis. CVS is generally recommended for the same reasons as Amniocentesis, and carries many of the same risks of associated miscarriage. The advantages of CVS testing over Amniocentesis are that it can be performed earlier than the Amniocentesis (between 10 and 12 weeks of gestation), and it offers better than 99% accuracy in detecting many genetic disorders and chromosomal abnormalities. A drawback of CVS is that neural tube defects are not detected.
You should consider your age, your previous medical history, and the medical history of your family when deciding whether or not to go forward with genetic testing during your pregnancy. Additionally, it is important to consider what positive results (indicating problems) would mean for you and your family. Many women would prefer to know in advance that they will have a baby with special needs, so they can prepare to meet those needs. Other women would prefer to not know. Discuss the options and risks associated with each of these tests with your doctor to decide which might be important for you.