Pregnancy Testing:

Blood Tests | Ultrasound | Amniocentesis | CVS

There are a number of tests used to screen for abnormalities in a developing fetus. According to the American College of Obstetricians and Gynecologists (ACOG), not all birth defects can be detected before delivery; however, certain tests can help to find some birth defects (Read about "Birth Defects") during pregnancy. Among the most common are ultrasound, amniocentesis and chorionic villus sampling (CVS).

Although prenatal tests can help to reassure prospective parents, it's also important to remember that no test can detect every problem, and also to keep in mind that some tests carry risks as well. Prenatal tests may also uncover problems that can't be corrected in the womb. On the other hand, prenatal testing does let parents prepare emotionally for potential problems and determine the most appropriate course of action for themselves and their family. The decision about which tests are most appropriate for a woman is one she needs to make after carefully considering all options with her doctor or midwife.

Blood tests

There are a number of blood tests that can be done during a pregnancy. You can be tested to find out which blood group you belong to. Your blood can also be tested to see if you are Rh negative. If a mother is Rh negative and her fetus is Rh positive, it can trigger Rh Disease. (Read about "Rh Disease") Your blood can also be tested for a number of other conditions such as anemia, Hepatitis B and HIV. (Read about "Anemia" "Hepatitis B" "HIV / AIDS")

The American College of Obstetricians and Gynecologists (ACOG) says first trimester (Read about "Stages of Pregnancy") blood tests for genetic defects are also an option. Blood tests for beta human chorionic gonadotropin (ß-hCG) and plasma protein-A (PAPP-A) combined with an ultrasound, called nuchal translucency that measures the thickness at the back of the neck of the fetus, can indicate an increased risk of Down syndrome (Read about "Down Syndrome") and the need for additional diagnostic testing. ACOG says all tests can result in false positives, and the decision to use these tests should be evaluated by a woman and her physician.

In the second trimester, the American Association for Clinical Chemistry (AACC) says that a blood test called the Triple Marker or Quad Marker Screen is often used. The test checks for alpha-fetoprotein (AFP) and two or three hormones - human chorionic gonadotropin (hCG); unconjugated estriol; and sometimes, inhibin A. These second-trimester blood tests can indicate a possible problem such as a neural tube defect (Read about "Neural Tube Defects"), or other issues such as multiple babies (Read about "Multiple Birth Pregnancies") or even something as benign as a miscalculation on the date of conception. (Read about "Due Date") AACC stresses that abnormal levels mean nothing in and of themselves; and that in only a very small percentage does it indicate a real problem. Abnormal test results however do indicate that more tests should probably be conducted.

Ultrasound

During an ultrasound (Read about "Ultrasound Imaging"), sound waves are used to produce what's called a sonogram or picture of the fetus. The March of Dimes says ultrasounds are performed for a number of reasons. Early in the pregnancy, they can be used to determine how old the fetus is and how many fetuses are present. In the second trimester, ultrasound can pick up certain structural birth defects such as missing limbs and spina bifida (in which the spine is not closing properly). (Read about spina bifida in "Neural Tube Defects") Ultrasound can also determine the sex of the child, and determine whether an appropriate amount of amniotic fluid is present. Ultrasounds later in the pregnancy can be used to check the well-being of the fetus and help determine if a cesarean or C-section may be needed to deliver the baby, either because the fetus is especially large, has a congenital defect or is in an abnormal position. A special form of ultrasound can also be used to detect heart problems in the fetus. (Read about "Congenital Heart Defects")

When the procedure is performed, a woman may be asked to make sure her bladder is full, which can be uncomfortable. (Read about "The Urinary System") Generally, ultrasound is produced by a device rubbed over the woman's stomach, and in most cases, a probe is inserted in the vagina. If an initial ultrasound detects potential problems, a more detailed exam may be scheduled. In addition, ultrasound cannot detect all structural birth defects.

According to the March of Dimes (MOD), ultrasound has been used for more than 30 years and no risks have been identified. However, it's not clear that low-risk pregnant women benefit from routine ultrasound exams. MOD says ultrasounds are OK when medically needed but casual use of ultrasounds should be avoided.

Amniocentesis

ACOG says amniocentesis is most commonly used in the second trimester to detect birth defects. Amniocentesis tests a small sample of the amniotic fluid surrounding the fetus. The March of Dimes says amniocentesis does carry a small risk of miscarriage, so it is not used routinely, but instead when there is an increased risk of chromosomal or genetic birth defects, such as fragile X syndrome (Read about "Fragile X Syndrome"), or certain malformations are suspected.

Amniocentesis can test for neural tube defects. (Read about "Neural Tube Defects") The neural tube is the part of the developing embryo from which the brain and spinal cord form. If it does not close properly during the fourth week after conception, birth defects such as spina bifida (a serious disability that results when the spinal column fails to close) and anencephaly (incomplete development of the brain and skull) may result. The U.S. Public Health Service says it's important for women of childbearing age to take 400 micrograms of folic acid a day, during and even before pregnancy, in order to help prevent neural tube defects. (Read about "Pregnancy and Nutrition")

Amniocentesis may be also used when a pregnant women is over the age of 35, since a woman's risk of having a baby with certain birth defects such as Down syndrome increases with age. (Read about "Later Age Pregnancy" "Down Syndrome") It may also be appropriate for women if they or a close family member has already had a child with a birth defect.

When amniocentesis is used, an ultrasound is performed to see exactly where the fetus is before the needle is inserted through the abdomen and into the uterus. This may cause cramping for the woman.

CVS

Another prenatal test is chorionic villus sampling or CVS. CVS can diagnose most, but not all, of the same birth defects as amniocentesis, but according to ACOG, CVS may pose a slightly higher risk of miscarriage and other complications. Some studies suggest it can also cause deformities in an infant's fingers or toes if it is done too early in the pregnancy.

A thin tube is inserted - through either a woman's vagina or her abdomen - to get a small sample of placental cells called chorionic villi. The procedure may cause cramping or discomfort.

CVS is most commonly used when parents want to know about chromosomal or other birth defects earlier in the pregnancy than amniocentesis. Like amniocentesis, it may be used when there is concern about a mother's age, or her own or her family history. (Read about "Family Health History") Unlike amniocentesis, CVS cannot detect neural tube defects, according to the American Academy of Family Physicians.

Healthy Pregnancy

While it's important to discuss the right tests needed during pregnancy, it's also important for a woman to do all she can to help prevent problems. (Read about "Healthy Pregnancy") That's why it's essential to see a doctor or healthcare provider as early as possible, preferably even before conceiving if you think you might become pregnant.

Related Information

    Pregnancy Resource Center

    Prenatal Care

    Pregnancy Terms Glossary

    Woman's Health Terms Glossary