Prenatal Tests

Prenatal Tests

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Testing 1, 2, 3

Not every prenatal test that your health-care provider suggests is necessary. We review the five you definitely need and give you the real deal on those you don’t.

By Judith A. Lothian, RN, PhD, LCCE, FACCE, and Charlotte De Vries Adapted from The Official Lamaze Guide: Giving Birth with ConfidencePrenatal Tests

These days, it can seem like your doctor has another round of prenatal testing every time you go in for an exam. OB/GYNs and midwives used to check only a few vital statistics throughout a woman’s pregnancy, but during the past 20 years, the extent of prenatal testing has increased dramatically. Yet not everyone in the medical community agrees that all of these extra tests are of value. Instead of being vigilant about picking up on problems, many health-care providers (doctors far more than midwives) over-test because they fear liability and simply expect trouble.

Many of these newer tests were created to diagnose problems in high-risk pregnancies. But with the increased medicalization of pregnancy, they have become routine for healthy women with no known risks. This does not mean that every test is right for everyone, however, or that they are risk-free themselves. There may be a problem that prenatal testing doesn’t show, or a problem may not exist even if the test suggests it does. Results that are unclear or even misleading can plague your peace of mind and decrease your confidence. The barrage of tests can also make you feel like your health-care provider knows everything there is to know about your pregnancy, which is not the case.

This list details the prenatal testing that is considered essential by everyone, as well as other tests that you’re likely to encounter during the next few months. You have the right to ask about and understand why each test is being recommended, the particulars of how a test will be done, all the risks associated with a test and if there are less risky approaches to diagnosing a problem or concern. Your health-care provider should let you know that you have a right to refuse a test, and he should welcome your questions and respect your decisions.

The Essentials

BLOOD PRESSURE CHECKS are necessary because rising blood pressure, especially in the last trimester, can indicate pregnancy-induced hypertension (also called preeclampsia or pretoxemia), which, if not treated, can be dangerous for you and your baby.

WEIGHT CHECKS make sure that you’re gaining enough weight for your baby’s health; they are not to keep you from gaining too much. And by tracking the growth of the uterus, your health-care provider can make sure that your baby is growing well. If your uterus gets larger more quickly than expected, it may indicate something quite different: multiples.

BLOOD TESTS identify a number of factors, including your blood type and cell count, iron level, immunity to chicken pox and other diseases, and Rh factor, as well as certain sexually transmitted diseases or infections. They are considered standard and acknowledged as important by all because they help establish your overall wellness.

FETAL HEART TONES can be monitored by your health-care provider with a fetoscope (a type of stethoscope) or handheld Doppler device. This test may reassure you that all is well, but your own knowledge of your baby’s movements throughout the day and night is equally important. There is no need for sonograms or electronic fetal monitoring to test these indicators.

The Others

CERVICAL CHECKS are invasive and provide little useful information on their own early in pregnancy, and there is no evidence that they should be a routine part of prenatal care. A pap smear can diagnose sexually transmitted diseases and other infections, but so can a blood test. The only time a cervical check may really help is if you are two weeks past your due date and your health-care provider is trying to determine if induction is appropriate.

ULTRASOUND EXAMINATIONS (sonograms) create a picture of a baby inside the womb using the sound waves that are produced by moving a transducer (like a computer mouse) across the mother’s abdomen. They are often used to determine a due date or to attempt to diagnose problems, but they are not always reliable. Misread sonogram results may lead to unnecessary or incorrect interventions.

For example, the nuchal translucency test uses ultrasound to measure the clear (hence, translucent) space in the tissue at the back of the baby’s neck. Doctors use this measurement to assess the baby’s risk for Down’s syndrome and other chromosomal abnormalities. But the diagnosis isn’t definite: The ultrasound isn’t directly testing for chromosomal problems or telling you for sure if your baby has normal chromosomes. Instead, it just gives you a better idea of the statistical likelihood that your baby will have a problem. Plus, a normal result isn’t a guarantee that everything is okay (just that a problem is unlikely), and an abnormal result doesn’t mean that your baby has a problem (just that he has an increased risk of one). It may only cause you unnecessary worry or, unfortunately, false joy.

Both the World Health Organization and the National Institutes of Health agree that routine ultrasound testing during pregnancy has not been sufficiently evaluated to go unquestioned. There is strong disagreement on the effect of ultrasound waves on a fetus. In fact, the Food and Drug Administration has declared that “prenatal ultrasounds can’t be considered completely innocuous,” and the American College of Obstetricians and Gynecologists says that casual use of ultrasound during pregnancy should be avoided.

CHORIONIC VILLUS SAMPLING (CVS) attempts to detect some birth defects by looking for chromosomal abnormalities. It is not routinely offered, but can be done at around 10 to 12 weeks to check for certain disorders, such as Down’s syndrome, in everyone who is tested. CVS also includes assessment for such conditions as cystic fibrosis or sickle cell anemia if your baby is thought to be at risk, but it can’t detect neural tube defects, such as spina bifida. There is a small chance of getting a false-positive (a result that incorrectly indicates that there might be something wrong), so CVS often leads to amniocentesis (see below) for confirmation. When the test is done too early in pregnancy, it has been associated with limb defects, such as missing fingers or toes, and miscarriage.

MATERNAL SERUM SCREENING TESTS, including the Alpha-fetoprotein and multiple marker tests such as triple screen, are done at 15 to 20 weeks to look for the presence of proteins or hormones in your blood that may signal a genetic or developmental problem in the baby. These screens have a high rate of false positives that are often discovered when further testing yields different results or when babies are born without problems. The results can cause unnecessary anxiety as well as more tests than needed.

You have a right to refuse these screens. Before you decide, think about what you would do with the results. If you don’t want to take the next step, amniocentesis (see below), it makes sense to consider not having these screens at all. If you have a family history of genetic diseases, including neural tube defects, you might consider them, but you can decline.

AMNIOCENTESIS is a procedure in which a needle is used to withdraw and test a small amount of amniotic fluid and cells from the sac surrounding the fetus. and tested to discover if the baby has Down’s syndrome or other birth defects. Many women, especially those over 35, are pressured to have this test. What may not be emphasized is that it is invasive and puts a woman’s body and baby at risk for infection, possibly causing bleeding, the leaking of more amniotic fluid, premature labor, fetal distress and even miscarriage.

Again, it is crucial to think about what you will do with the results before you agree to an amniocentesis. If the information will not change the course of your pregnancy in any way, then the test may not be worth having. However, you may find it helpful to know in advance that your baby might have a problem. Decide what’s best for you.

GLUCOSE SCREENING is a test for gestational diabetes, which is diagnosed in about 5 percent to 7 percent of women. Taken at 24 to 28 weeks, you drink a special sugar mixture, or eat a standardized dose of jellybeans, and an hour later, a blood sample is drawn and measured for its glucose level. If it’s too high, you may have gestational diabetes. It’s important to know, however, that your baby needs glucose, which helps him grow and develop. 

GROUP B STREPTOCOCCUS (GBS) is a type of bacteria that lives in the vagina and rectum. Many women carry GBS and do not have any symptoms. GBS can be passed to a baby during birth. Most babies who get GBS from their mothers do not have any problems. A few, however, become sick. This illness can cause serious health problems and even death in newborn babies. GBS usually can be detected with a routine screening test that is given between 35 weeks and 37 weeks of pregnancy. For this test, a swab is used to take samples from the vagina and rectum.

For most GBS positive women (90 percent of all pregnant women who are GBS positive), one dose of antibiotic is effective in reducing the exposure of the baby to the bacteria during labor. If labor is preterm, if your membranes ruptured more than eighteen hours ago, or if you have a fever in labor, the risks are a bit higher but at least one to two hours of antibiotics during labor significantly reduces the risk of GBS newborn infection.

You Decide

Midwives in the Netherlands use the term “spoiling the pregnancy” for the unnecessary worry that the false-positive results of prenatal testing can have on a mother-to-be, says Barbara Katz Rothman, author of Recreating Motherhood (Rutgers University Press). They understand that this misinformation may rob you of joy, peace and a relaxed relationship with the baby you’re carrying inside of you.

So keep that in mind as you’re choosing from the menu of tests presented to you. Routine prenatal testing can medicalize your pregnancy and rob you of your confidence. It may make you feel that your health, happiness and baby’s perfection is ensured, or it may scare you into believing that your baby won’t be born healthy. Either way, prenatal testing cannot guarantee any specific outcome, so it may not be worth the extra emotions it brings.

If you refuse to have some prenatal testing done, remember that you are not the first or the last woman to make this choice. Not everyone needs or wants to know that there may be problems with their baby, and many women don’t want the false alarms and worry. What your doctor sees as an absolutely necessary test may not be what a midwife sees. And it may not be what you see either.

Additional important information:


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