Prenatal Testing 101
What New Parents Should Know

If you’re receiving quality prenatal care, testing is as much a part of your pregnancy as morning sickness, maternity clothes and swollen ankles. The findings can provide valuable insights regarding your health and your baby’s health and, in some cases, indicate the need for treatment that could save the life of your unborn child.

Tests to Consider Before Getting Pregnant

Many existing conditions that could be problematic for you and your baby during pregnancy can be treated and very often cured. That’s why it’s a good idea to schedule an appointment with your obstetrician/gynecologist before becoming pregnant to discuss your medical history and what tests might be right for you. This could include blood tests for both partners to check for the following:

Hepatitis B, syphilis and HIV
Immunity to rubella (German measles)
Genetic factors that could lead to diseases in children born to you and your partner, including cystic fibrosis, Tay-Sach’s disease (in those of Eastern European Jewish descent) and sickle cell anemia (in those of African-American and Mediterranean descent)

Women should also undergo a Pap smear to test for cervical cancer. Pap smears can also be used to detect Chlamydia and gonorrhea.

Your First Prenatal Visit

If you did not undergo the aforementioned tests before pregnancy, you can expect them during your first prenatal visit (and, in some cases, they may be repeated). In addition, you will undergo blood tests to check for the following:

Your blood type and Rh (or rhesus) factor, which is a protein substance found in the blood of 85 percent of the population. If you have the protein, you are considered Rh positive; if you don’t, you are Rh negative. If the mother is Rh negative and the child is Rh positive, the mother must be treated to avoid problems in the baby, including anemia, brain damage and even death. If doctors suspect the baby’s Rh factor is positive, shots of rhogan are administered at 28 weeks’ gestation.
Anemia. Women who remain anemic during their first two trimesters are at a higher risk of preterm delivery or having a low birth weight baby. Anemia can be treated with dietary supplements.

The doctor or nurse will also do the following at your first visit and subsequent visits:

Use fetal Doppler equipment to listen to the baby’s heartbeat
Administer a urine test, which will determine if you have a urinary tract infection

A glucose tolerance test (see below) may be performed if you previously had gestational diabetes, are obese, have had a child weighing more than 9 pounds, have a family history of diabetes or meet other criteria established by your physician.

Urine test: (performed at every visit) to evaluate glucose and protein levels, which could be indicators of gestational diabetes and require that you take the glucose tolerance test earlier in your pregnancy than is normally indicated.
Glucose tolerance test: (performed between 24 and 28 weeks’ gestation) to check for gestational diabetes. This involves drinking a very sweet substance, waiting an hour and then having blood drawn.
Group B streptococcus screening: (performed between 35 and 36 weeks’ gestation) to see if you have a bacteria that, if left untreated, could prove harmful to your baby. The screening is performed by swabbing cells from the lower end of the vagina and rectum. If you test positive, antibiotics will be given to you during labor.
Ultrasound tests: (performed between eight and 20 weeks’ gestation; frequency can vary) to make sure baby is growing normally, verify expected delivery date, assess amount of amniotic fluid and indicate position of placenta (this occurs later in the second and third trimesters). Depending on the expectant mother’s risk factors (e.g., age, medical history), doctors may order what is called a level II ultrasound, which provides more detailed information. At some medical centers, three-dimensional ultrasound is available, which can be helpful to parents at risk for having children with soft tissue anomalies, such as cleft lip and anomalies of the hands and feet.
Cervical measurement: (between 16 and 20 weeks’ gestation) via ultrasound can help doctors determine if a woman is at risk for preterm delivery. If the findings indicate it’s a possibility, doctors recommend behavior modification and, if necessary, plan for a C-section.

Special Prenatal Tests

If you are 35 or older or have a history of genetic anomalies, your doctor may recommend special screening or diagnostic tests. Diagnostic tests provide definitive answers regarding many genetic disorders, including Down syndrome, cystic fibrosis and Huntington’s disease. Screening tests do not provide definitive answers; rather, they indicate the likelihood that a child will be born with certain genetic disorders, such as Down syndrome, trisomy 18 and trisomy 13. If a screening test indicates a problem, diagnostic testing is usually recommended.

A woman wishing to have her fetus tested for genetic disorders may undergo one or more of the tests listed below, depending on her situation and the physician’s recommendation.

Screening Tests

First Trimester Screening Test
The first trimester screening test involves taking the pregnant woman’s blood and measuring the levels of two key proteins found in pregnant women, plus using ultrasound to measure skin thickness behind the neck of the fetus (called “nuchal translucency”).

Quad Screen
The quad screen (typically done between 15 and 20 weeks’ gestation) also involves a blood test, which evaluates four components of the blood (there is also a triple screen, which evaluates three components).

Integrated Screen
The integrated screen combines components of the first trimester screen with the quad screen to provide a more complete picture than one screen can provide. This test is just starting to become more commercially available.

Diagnostic Tests

Chorionic villus sampling (CVS)
Chorionic villus sampling (CVS) can, with almost 100 percent certainty, indicate whether a baby has or does not have Down syndrome. CVS is performed between 11 and 13 weeks’ gestation. In most cases, doctors insert a thin tube through a woman’s vagina and cervix and remove a small sample of tissue, which is then sent to a lab for evaluation. Risks include miscarriage (between 1 in 200 and 1 in 100 women miscarry after CVS) and the slight possibility that the unborn child’s limbs will be injured during the procedure.

Amniocentesis
Amniocentesis indicates whether or not a baby has Down syndrome, but it can’t be performed until the second trimester. Like CVS, its results are almost always correct. Using ultrasound to guide them, doctors insert a needle into the sac surrounding the baby and remove amniotic fluids for evaluation. For most women, discomfort is minimal. Risks include miscarriage (1 in 300) and loss of amniotic fluid. Loss of fluid resolves itself in most cases but can cause complications such as infection, preterm delivery and possible pregnancy loss.

There’s no doubt, prenatal testing can be overwhelming. The information the tests provide, however, can be empowering during this exciting time in your life and can prepare you for the doctor’s visits ahead.

Editorial provided by maternal-fetal medicine specialist Xavier Pombar, DO, a private practice physician at the RUSH Fetal and Neonatal Medicine Program. Dr. Pombar and his colleagues specialize in helping women who are facing high-risk pregnancies.