Is My Baby Healthy? A Guide to Prenatal Testing

I was sitting in a small room trying to chat comfortably and ignore the needle in my arm when the nurse asked, do you want us to call you with the results of the blood test, or just send them to the doctor.

I was in my 18th week of pregnancy, and flabbergasted by the question. “Will I know what the results mean,” I asked. Going a little red I admitted, “I don’t even know what I’m being tested fo r.”

It’s my fourth pregnancy, so when my doctor said, “Go get your blood drawn,” I obediently went. I am, after all a very good pregnant lady, taking my prenatal vitamin every day, eschewing caffeine, and faithfully doing yoga for pregnant women.

I like to leave all the fancy medical terminology and the worries that go with it to my doctor. When a week later, the doctor told me the tests were normal, I breathed a sigh of relief, though I wasn’t quite sure what bullets my baby and I had dodged. As I left the clinic, however, I vowed to become better informed.

The four tubes of blood I’d given were used to type my blood and for the triple screen test (also known as multiple marker screening and AFP plus). The test is used to project the probability of genetic birth defects like Down’s syndrome or spina bifida.

The test looks at the levels of three specific substances in the blood, alpha-fetalprotein, human chorionic gonadotropin and estriol. The results are combined with the mother’s age, weight, ethnicity and gestation of pregnancy in order to assess probabilities of potential genetic disorders. It is very important when reading the test to know the age of the fetus, since the levels of these substances considered normal changes as pregnancy progresses.

Abnormal test results don’t automatically mean a baby will have a birth defect. The test has a very wide range of abnormal results to prevent missing a fetus that has a serious condition. These tests DO NOT diagnose a problem; they only signal that further testing should be done.

Recently, prenatal screening tests have also become available in the first trimester as an option for patients who are known to be at a high risk for having babies with birth defects because of age or a family history of birth defects. The testing combines maternal blood tests with an ultrasound evaluation.

After an abnormal triple screen, a doctor may recommend an amniocentesis or chorionic villus sampling.

Chorionic villus sampling, (or a CVS) is done in the first trimester and is also recommended to those patients whose medical histories reveal a higher possibility of birth defects. It can also be used to determine paternity. It is usually performed between 10 to 13 weeks. CVS is a diagnostic procedure that involves removing some chorionic villi cells from the placenta at the point where it attaches to the uterine wall. The American Pregnancy Association describes the two different ways samples can be collected.

Transcervical: An ultrasound guides a thin catheter through the cervix to your placenta. The chorionic villi cells are gently suctioned into the catheter. This is the most common method.

Transabdominal: An ultrasound guides a long thin needle through the abdomen to your placenta. The needle draws a sample of tissue and then is removed. This procedure is similar to that of amniocentesis.

While chronic villus sampling can be performed earlier in the pregnancy to sooner identify genetic problems, it has a slightly higher risk of miscarriage than an amniocentesis (1-3 out of 100 cases).

Similar to a chronic villus sampling, but more widely known, is an amniocentesis. Amniocentesis detects chromosome abnormalities, neural tube defects and genetic disorders.  It is performed between 14 and 20 weeks. An ultrasound is used as a guide to determine a safe location for a needle to enter through the mother’s belly into the amniotic sac so the fluid may be safely removed. A sample of amniotic fluid is collected through the needle.

Down syndrome or Trisomy 21 is the most common chromosome abnormality it detects. Genetic disorders include disorders like cystic fibrosis. The most common neural tube defect is spina bifida. An Amniocentesis is occasionally used late in pregnancy to assess whether the baby’s lungs are mature enough for the baby to breathe on his own.

An amniocentesis is 98 percent accurate in determining if chromosomal defects are present, however, it cannot determine the severity of the associated birth defects.

Although an amniocentesis is a fairly common procedure, there are some risks associated with it. The risk of miscarriage is 1 to 2 out of 200. After the procedure the mother may experience cramping, leakage of fluid, or minor irritation around the puncture site.

Though pre-natal testing can cause anxiety, these tests are performed by experienced professionals hundreds of thousands of times each year. Being informed about the procedures can help ease the apprehension.

For more about prenatal testing visit American or Baby .