Testing, Testing

TESTING, TESTING
THE FAMILY GROOVE’S ON-CALL OB/GYN, DR. RANDY FINK,
TAKES YOU ON A JOURNEY THROUGH YOUR PREGNANCY
—ONE TEST AT A TIME

Let’s begin by establishing that we calculate your due date as 40 weeks from the first day of your last menstrual period. If you count, this is 10 months—not nine months! Therefore, we always refer to how many weeks you are pregnant, never how many months.

THE FIRST TRIMESTER
At your first visit (what we call your New OB visit), we perform a complete checkup and a group of blood tests.
During your exam, it is important to do the routine things, like listen to your heart and lungs. A breast exam is an important part; it gives us the chance to review the normal changes you can expect in your breasts during pregnancy and to encourage the idea of breast-feeding. We usually perform a pap smear, which is a screening test for pre-cancers of your cervix. With this, we can also test for infections in your cervix that you may not know about but that can affect your baby. These are usually sexually transmitted infections, such as gonorrhea and chlamydia. We’ll also want to feel the size of your uterus and the shape of your ovaries. Some clinicians will perform an ultrasound exam to see the baby’s heartbeat, but by 12 to 13 weeks, we can usually hear the heartbeat by listening through your abdomen with a special instrument known as a Doppler.

The blood tests include confirming your blood type and a blood count to check for anemia. We test for a number of types of infections in a mom’s blood that can affect a baby, like hepatitis B, syphilis and HIV, as well as ascertain whether you are immune to rubella, an infection for which you have been vaccinated. Some clinicians will test your thyroid hormone level, presence of the herpes virus, and to see whether you are immune to chicken pox. We also have the lab perform a culture of your urine to screen for bacteria.

THE SECOND TRIMESTER
In the early second trimester, there are a number of opportunities for genetic testing. This testing is designed to identify chromosome problems in your baby, such as Down syndrome. Women who are 35 or older at the time of delivery are considered at higher risk for having a baby with chromosome abnormalities, but these chromosome problems can occur in a woman of any age. The classic testing is an amniocentesis, in which your doctor places a needle through the skin of your abdomen and tests the fluid that surrounds your baby. That fluid has some of the baby’s sloughed skin cells, and from these cells the laboratory can tell us some details about your baby’s genetics. The amniocentesis is usually performed between 15 and 17 weeks of pregnancy. There is also an earlier test available, known as CVS, or chorionic villus sampling. This test takes some cells from around the placenta and can give the same information about chromosomes. The advantage to this test is that it is performed between 11 and 13 weeks, so results come back much earlier. Again, these invasive tests were classically offered to women age 35 and older. Recently, recommendations have changed. Now, invasive testing is appropriate for some women under 35, too, while women 35 and over may consider noninvasive testing.

WHAT IS A NONINVASIVE TEST?
Noninvasive tests are considered screening tests. They are designed to select out moms who should have the more invasive tests performed. This is the difference between a screening test and a diagnostic test. Diagnostic tests, such as amniocentesis and CVS, are more than 99 percent accurate. Screening tests, however, are far from perfect. They have a rate of both false positive and false negative results. The older test, and still the only one offered in many places, is called the AFP. AFP stands for alpha-fetoprotein. The test itself is actually a combination of several different hormone levels from a mother’s blood, and is designed as a screening test for chromosomeproblems and certain types of spinal birth defects. The AFP is done at about 16 weeks of pregnancy. An improvement on the AFP is called the sequential screen. It is done in two steps. First, a series of hormone levels are drawn from the mother’s blood at about 12 to13 weeks’ gestation. This is combined with an ultrasound to measure the thickness of the baby’s neck. These results are plugged into a computer. If they are abnormal, the screening test is over and Mom is referred for diagnostic testing. If they are normal, a different hormone blood test is drawn from the mom about a month later. This result is combined with the earlier results, and taken together, the test is more accurate with a lower risk of false positives. Most insurances are covering this updated screening now, and I encourage all pregnant women to ask their OB about it.

THE SONOGRAM
Most pregnant women will have a sonogram between 16 and 20 weeks to screen for different types of birth defects. The gender of the baby can usually be determined at this point as well. Many people ask about “the ultrasound to find out the sex of the baby.” While determining the sex is usually possible, the purpose of this ultrasound is really to make sure that a number of features in the baby’s anatomy appear normal.

THE GLUCOSE TOLERANCE TEST
Between 24 and 28 weeks, mothers take the screening test for gestational diabetes. This test may also be known as “the one-hour test,” the glucola or the diabetic screen. Gestational diabetes is a disease of pregnancy that can affect any mother, even if she has no personal or family history of diabetes. The hormones of pregnancy can cause difficulties for a mom’s body to handle sugar, which in turn results in problems for the baby. The screening test is easy: Mom drinks 50 grams of a sugary drink (it comes in different flavors and is provided by the lab). One hour later, Mom’s blood is drawn. If the result is above 130 to 140, then Mom needs a diagnostic test. The diagnostic test is called the three-hour glucose tolerance test and requires four blood tests. Mom must be fasting for the test, and she has her first blood sugar level drawn before she drinks double the amount of the sugary drink (100 grams). Her blood sugar is then tested once each hour for the next three hours. Having two of the four blood tests abnormally high is diagnostic of gestational diabetes.

Often, we repeat a blood count for anemia at the same time as the diabetic screen, and some states require a repeat of the tests for HIV and syphilis.

THE THIRD TRIMESTER
At every prenatal visit, we check Mom’s blood pressure and test her urine for evidence of infection or other problems. We listen to the baby’s heartbeat and measure the height of the uterus on Mom’s belly. Usually, we start doing vaginal exams at about 36 weeks to see if the cervix is getting ready for delivery. The final laboratory test is performed around the 36-week visit as well. This is a test for a type of bacteria known as Group Beta Strep (GBS).

GBS is a bacteria that colonizes the vagina and sometimes the bladder in up to 40 percent of women. The presence of Mom’s GBS is associated with infections in newborn babies, so intravenous antibiotics (i.e., penicillin) are given to a woman in labor whose GBS test was positive. Testing for GBS is simple. A cotton swab like a Q-tip is momentarily placed in the vagina, around the perineum, and in the rectum. This swab can be cultured for the bacteria.

Pregnancy is an exciting and challenging time! I hope this helps unravel some of the mysteries of testing!

For more information about Randy A. Fink, MD, FACOG, please go to www.drrandyfink.yourmd.com.