ABCs of Prenatal Testing
By Brette McWhorter Sember

Prenatal testing can offer you answers and reassurances, but it can be hard to know just what exactly you’re being tested for and how the tests work. If you are over age 35, the National Society of Genetic Counselors recommends that you meet with a genetic counselor before undergoing screening tests during pregnancy.

Initial Tests
What: You’ll be given a long scrip for blood work at your first appointment. Don’t be alarmed – all the tests are done with only one needle prick and a few vials of blood. These tests will give your physician information about your blood type, Rh factor (negative or positive blood type), anemia, syphilis, Hepatitis B, HIV, immunity to things like measles and chickenpox, and cystic fibrosis. You’ll also get a Pap smear to check for cervical cancer and STDs. Sickle cell anemia testing is ordered for women of African or Mediterranean descent. Urine tests are routinely performed at every prenatal visit to check the urine for protein (which can signal preeclampsia) and sugar (an indication of gestational diabetes). “The first visit, and blood work, are probably most important of all,” says Dr. Edmund Funai, chief of obstetrics at Yale-New Haven Hospital.

Who: These tests are routinely done for all women

When: At your first prenatal visit, you’ll be given the scrip and asked to go as soon as possible for the testing. Urine testing will be done at each appointment.

Additional Blood Tests
Throughout your pregnancy, you may be sent for additional blood work to test for a variety of conditions.

Gestational Diabetes
What: Screening is done with a blood test after you have fasted and then drunk a special glucose drink. Gestational diabetes is an issue for a small percent of women and can have dangerous consequences for the baby. Dr. Funai reports, “15% test positive and need further testing, but only 30% of these will have diabetes.”

When: Routine testing takes place between 24 and 28 weeks, but if you are obese, had a previous baby over nine pounds, are over 30, or have a family history of diabetes, you may be tested at 12 weeks. If you test positive, you may be sent for a test that requires several blood draws over the space of a few hours.

Who: All women are routinely screened.

First Trimester Assessment & Triple/Quad Screening
What: First trimester assessment is a blood test that screens for trisomy 21 (the chromosomal abnormality known as Down’s Syndrome) and trisomy 18 (another chromosomal abnormality). Triple, quad, or AFP testing are blood tests that are done later in pregnancy used to further evaluate the risks for these problems, as well as spina bifida. These tests can be done by themselves, or in conjunction with an ultrasound, and latest recommendations show that combining both first trimester and second trimester blood work with an ultrasound gives the best results. “The AFP-Quad tests detect approximately 85% of all cases of trisomy 21 with only a 7% false positive rate,” says Dr. Stephen Carr, Associate Professor of OB/GYN at Brown University. What is essential to remember about this test is that it only identifies a risk factor, it does not diagnose Down’s Syndrome or other disorders. You don’t get a yes or no result, you get a result that categorizes your risk – like one in 2000 or one in 400.

When: Dr Carr says, “If a woman wants the earliest possible answer, then I recommend first trimester screening with blood work and ultrasound at 11 to 14 weeks. If she wants the best, then I recommend first trimester screening with bloodwork and ultrasound at 11 to 14 weeks combined with AFP-Quad testing. That combination, the full and integrated screening, yields the best performance, and gets results to the woman as early as 16 to 17 weeks.”

Who: Jill Allen Fonda, board member of the National Society of Genetic Counselors, says, “All women are now offered one of these tests, but the current recommendations do not specify which test must be offered.” Women over age 35 have a higher risk of Down’s Syndrome and may be encouraged to have the test. If you’re considering the test, Dr. Carr recommends that you first evaluate what you are going to do with the information it will provide.

Ultrasound
What: Ultrasounds bounce sound waves off the baby’s bones and tissue to form an image of the baby. Ultrasounds are used to determine or confirm due dates, look for multiple babies, check the baby’s development, record heartbeats, measure the amount of amniotic fluid, and screen for abnormalities. Ultrasounds have no impact on the baby and are usually not uncomfortable, although needing to have a full bladder for the test is the biggest complaint by women. Finding out the baby’s sex can be one of the perks of this test, if you want the information. A special ultrasound, called a nuchal translucency test, is used in conjunction with a triple or quad screen (and sometimes first trimester blood work) to evaluate the risk for Down’s Syndrome.

When: The first ultrasound is usually around 18 to 20 weeks (although some are done earlier to date a pregnancy or check for twins). Later ultrasounds may be done to check positioning of the placenta, to estimate birth weight, or during amniocentesis. Immediate results are often shared, but it may take a week or two for a report to be written.

Who: “Ultrasound is not recommended as a routine procedure by any US professional organization, however, it has become common practice in most of the US and performed on almost everyone,” points out Dr. Jacques Abramowicz, Director of Ob/Gyn Ultrasound at Rush University Medical Center. High risk pregnancies may require high resolution or 3D ultrasounds.

Chorionic Villus Sampling (CVS)
What: A thin tube is inserted through the vagina and cervix to take a sample of the chorionic villi, wisps of tissue that attach the placenta to the wall of the uterus. The sample is then tested for Down’s Syndrome and other chromosomal abnormalities (note that this test cannot test for neural tube defects, but that amniocentesis can). It has a higher risk of miscarriage than amniocentesis (between .5 and one percent according to the March of Dimes).

When: It is performed at 10 or 11 weeks (a month sooner than amniocentesis) with results in one to seven days.

Who: This test is used if a first trimester screening indicates a risk of chromosomal problems, a woman is at a higher risk for these, and waiting for an amniocentesis is not advised.

Amniocentesis
What: The amnio is probably the most feared prenatal test, but it takes approximately a minute, and the needle is thinner than the one used to do a regular blood test. Your physician will use ultrasound to help guide the needle and will take about one ounce of amniotic fluid to be tested. Some women feel cramping or a pinch during the procedure. This test diagnoses Down’s syndrome, spina bifida, and anencephaly conclusively and can also verify the baby’s sex. Many women are concerned about the risk of miscarriage after an amnio. That risk has been reported to be one in 400, but a recent study showed that when the test was done by a skilled practitioner, the risk was only one in 1000.

When: This test is done at 16 to 18 weeks with results within a few days or weeks.

Who: In general, you should only have an amnio if screening tests have indicated that your risk of an abnormality is higher than the miscarriage risk of the amnio.

Non-Stress Test
What: The baby’s heart rate in response to movements he or she makes is monitored to determine if the baby is getting enough oxygen and to make sure the nervous system is responding. If the baby is asleep, a noise may be used to wake him or her up.

When: This is done after the 26th or 28th week.

Who: Non-stress tests are ordered when there is a concern about fetal movement, or if the pregnancy is high risk.

Contraction Stress Test
What: The mother is given pitocin to create uterine contractions. The effect of the contractions on the baby’s heart rate is measured and used to determine how the baby will respond to labor contractions.

When: When it is determined by the physician that it is necessary.

Who: This test is usually ordered if a non-stress test has not provided reassuring results.

Group B Strep (GBS)
What: Group B Streptococcus is a bacteria that, if present in the mother’s vagina, can indicate an infection in the baby and can cause preterm labor. The test is done by swabbing the inside of the vagina with a long cotton swab. Dr. Funai says, “30% of all women carry GBS. In many cases, it can be passed to the baby, and if untreated, 1% will get very sick. Screening for GBS, and giving antibiotics in labor, can reduce 86% of this disease.” GBS is easily treated with antibiotics.

When: Between the 35th and 37th week.

Who: This test is routinely done on all women.

Percutaneous Umbilical Blood Sampling (PUBS)
What: Although the long name makes this procedure sound awfully dire, it is a very simple procedure in which a physician (using ultrasound) guides a needle into the umbilical vein to sample the baby’s chromosomes and test the baby for anemia. This test is very quick, with the same sensation as amniocentesis and offers quick results. The American Pregnancy Association reports the miscarriage risk at one or two percent.

Who: This test is recommended for women who have had an abnormal ultrasound, who have an inconclusive amnio result, for moms who are exposed to infectious diseases during pregnancy, or babies who have Rh disease.

When:18 to 36 weeks, with results in three days.

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