Sidebar: Diagnostic Tests Of The Third Trimester
By Peggy O'Mara
Issue 120, September/October 2003
Fom the book Mothering Magazine's Having A Baby, Naturally: The Mothering Magazine Guide to Pregnancy and Childbirth edited and published by Peggy O'Mara with Wendy Ponte. Copyright © 2003 by The Philip Lief Group, Inc. and Mothering Magazine, Inc. Reprinted by permission of Atria Books, an imprint of Simon and Schuster, Inc.
Birth goes best if it is not intruded upon by strange people and strange events. It goes best when a woman feels safe enough and free enough to abandon herself to the process.
-Penny Armstrong and Sheryl Feldman, A Midwife's Story
Even if you have not given birth before, you are probably already familiar with the terminology of prenatal testing. Words like sonogram and amniocentesis have become a familiar part of our general vocabulary.
There is a good reason for that familiarity. It is because many of these prenatal tests, originally created to test certain high-risk pregnancy situations, have become standard practice for all pregnant women. While you may think that these tests can do no harm, some of them have never been thoroughly studied for safety to mother and baby, and may present physical risks to both. Relying on prenatal tests to ease your concerns may also create an atmosphere of worry and anxiety, just what you had hoped to avoid by taking them. Results can sometimes be vague and, what's worse, misleading.
As long ago as 1974, the American College of Obstetricians and Gynecologists (ACOG) recommended that its members take great care to obtain informed consent from their patients before proceeding with any tests or treatments. ACOG was careful to distinguish between consent and informed consent. In other words, patients should fully understand what will happen to them and their unborn children before proceeding blindly with any type of testing or treatment. This is particularly important now, years later, since many tests are prescribed by physicians who assume that their patients understand what the tests are meant to assess, as well as their risks to mother and baby.
Informed consent means much more than just showing up for a scheduled ultrasound or amniocentesis. You have the right to:
Understand in detail how the procedure is administered.
Understand all the risks associated with it.
Know what the alternatives are: is there another test or procedure that poses less risk?
Carefully consider the physical and emotional impacts.
Feel free to say no to any tests you don't feel are necessary.
Before you can decide to give informed consent, you need to understand the tests and procedures that are routinely administered during pregnancy-ultrasound, the triple screen, amniocentesis, and chorionic villus sampling.
Ultrasound, or sonogram, was originally developed during World War II to detect enemy submarines. This diagnostic technique has replaced X rays, now known to be dangerous, as the method of choice to view a baby inside the uterus. Ultrasound uses sound waves to create a two-dimensional image of the baby that is suitable for viewing.
Why Is Ultrasound Used? Ultrasound is used in two ways. One is to investigate a specific concern. If a woman has a family history of a medical condition, or if another test indicates risk, an ultrasound may be recommended. More commonly, however, ultrasound is used as a routine procedure performed on almost every pregnant woman to screen for potential problems, even if she is not at any particular risk.
How Is Ultrasound Done? During ultrasound, a device called a transducer that produces high-energy sound waves is either run across your belly or, in very early pregnancy, inserted into the vagina, where a heartbeat can be detected earlier. The sound waves then rebound and are converted into a visual image of the fetus.
Ultrasound may be done in your practitioner's office, or you may be sent to a hospital. You will usually be asked to have a full bladder for this procedure, depending on the reason for the ultrasound (checking for placenta previa, which we discuss later in this section, requires an empty bladder, for example). You will lie down on a table and will be asked to remove your pants and pull up your shirt or dress to expose your belly for an abdominal ultrasound. You will need to undress from the waist down or wear a gown for a vaginal ultrasound.
For an abdominal ultrasound, a gel will be squirted over your belly to facilitate the movement of the paddle-like transducer across it. For a transvaginal test, the lubricated wand will be gently inserted into your vagina. The transducer is then moved around until the operator or doctor finds the appropriate view.
Most ultrasound exams last only a few minutes. The procedure is painless, though your full bladder may cause you some discomfort. You will usually be able to see the monitor as the test is being done. How much information you are given during the procedure itself will depend on the operator. If your midwife or doctor is present, you will most likely be able to ask questions. Most technicians, though, have been trained to tell the patient nothing until your midwife or doctor reviews the results. Sometimes it is possible to have copies of the ultrasound pictures.
Other uses of ultrasound include the Doppler, or Doptone, a small handheld device used to hear the baby's heartbeat after the tenth week, and electronic fetal monitors (EFMs), used by most hospital maternity wards to monitor the baby's heart rate during labor.
When is Ultrasound Necessary? Ultrasound diagnosis has important uses in pregnancy:
To quickly establish whether or not a fetus is still alive.
When there is early bleeding, to predict if a miscarriage is happening.
To confirm a suspected ectopic pregnancy (where the egg has implanted into a fallopian tube rather than the uterus), a blighted ovum (where a sac grows without an embryo inside it), or a molar pregnancy (where a "false" pregnancy grows inside the uterus), when used in conjunction with other tests.
To determine the position of the baby during procedures such as amniocentesis and chorionic villus sampling (discussed below).
To establish whether or not levels of amniotic fluid are still adequate in the late weeks of pregnancy.
To ascertain the position of the placenta at the time of birth if a low-lying placenta is suspected.
Generally speaking, ultrasound is more accurate to explore a specific situation such as those above than when used in a generalized, routine way, in part because highly trained technicians and better machines are used to detect suspected problems.
If an ultrasound is necessary, check on the experience of the operator. Choose someone who has a high level of skill and experience (about 750 scans per year), since a license is not required to operate an ultrasound machine.
When Is Ultrasound Unnecessary? According to ACOG, the country's leading group of obstetrical experts, ultrasound is not necessary for every woman or in every pregnancy, and is not recommended for routine use. Despite this recommendation, ultrasound is used routinely in as many as 70 percent of pregnancies in the US.1 Here are the common reasons that ultrasound is used routinely:
To estimate the baby's due date. Done prior to 18 weeks, it is most accurate (after this, it is accurate only within a week either way).
To look for physical abnormalities. Many major abnormalities, such as Down syndrome, cerebral palsy, and heart or kidney problems, most likely won't show up on an ultrasound.
To confirm multiple fetuses. Ultrasound is reliable in confirming multiple fetuses only when other heartbeats have already been detected with a stethoscope.
For verification of a breech position. This occurs when the baby is lying in a feet- or buttocks-first position near the end of pregnancy, rather than head down. A qualified midwife or doctor can diagnose this simply by palpating the mother's belly.
To screen for intrauterine growth retardation (IUGR). IUGR is a condition where the baby is not growing in the womb as it should.
Location of the placenta during pregnancy. A very low-lying placenta (a condition called placenta previa) puts the mother at risk of severe bleeding during labor, and usually necessitates a cesarean section. However, 19 out of 20 cases of placenta previa detected by ultrasound in the second trimester correct themselves as pregnancy progresses.
While routine screening for the above problems is not recommended, ultrasound may be necessary to confirm a problem that has been detected by other tests.
How Effective Is Ultrasound? The effectiveness of ultrasound as a routine procedure has never been proven. In fact, a number of studies have shown definitively that there is no better outcome for women who have had one or more routine ultrasound examinations during their pregnancies, as compared to those who have had none.2 It is, as well, a very expensive procedure, costing the US more than a billion healthcare dollars per year.
According to Australian physician and ultrasound authority Sarah Buckley, MD, there is no evidence that ultrasound is necessarily more accurate at estimating due date than hands-on palpation done in conjunction with a woman's own guesstimate of her due date, even if the woman is unsure of when she conceived. Palpating the mother's belly can also accurately diagnose a breech position, and a stethoscope can be used to detect multiple fetuses. In addition, a stethoscope or fetoscope is as effective as a Doppler in detecting fetal heart tones after 16 weeks.
When used routinely, ultrasound also has a very high rate of false positives. In some instances, normal babies are aborted because of a false positive diagnosis. A United Kingdom study found that 1 in 200 babies (0.5 percent) aborted for major abnormalities after a positive ultrasound result were, in fact, normal babies.3
In one Swedish study conducted at Uppsala University, ultrasound screening for IUGR is compared to a midwife's repeated measuring of the uterus in 581 pregnancies.4 The report concluded that the midwife's measurements were more accurate than the ultrasound measurements. Dozens of additional studies in the US, England, and Sweden have come to the same conclusion. According to Dr. Marsden Wagner, perinatal epidemiologist and former head of the Responsible Office for Maternal and Child Health for the European Office of the World Health Organization, more than 50 percent of ultrasound screenings for IUGR give false positive results.
A recent study at a major women's hospital in Brisbane, Australia (where 99 percent of women receive routine ultrasounds), showed that routine ultrasound missed about 40 percent of abnormalities.5 A 1989 study conducted by ACOG revealed that ultrasounds miss abnormalities just as often as they give false positive readings. In the ACOG study, 51 percent of ultrasounds failed to reveal a serious problem when it actually did exist.6
Is Ultrasound Safe? The National Institutes of Health cautions against routine use of ultrasound, noting that "the data on clinical efficacy and safety do not allow recommendation for routine screening at this time; there is a need for multidisciplinary randomized controlled clinical trials for an adequate assessment."7
Similarly, the World Health Organization (WHO) urges prudence: "Ultrasound screening during pregnancy is now in widespread use without sufficient evaluation. Research has demonstrated its efficacy for certain complications of pregnancy but the published material does not justify the routine use of ultrasound in pregnant women."8
According to perinatal epidemiologist Marsden Wagner, the safety of ultrasound has never been clinically proven. The editors of the Cochrane Database, a review of over 9,000 controlled trials from 85 different countries, note that "there has been surprisingly little well-organized research to evaluate possible adverse effects of ultrasound exposure on human fetuses."9
In a 1999 study, six scientists at University College Dublin found that ultrasound creates changes in cells. Patrick Brennan, the lead researcher, said, "It has been assumed for a long time that ultrasound had no effect on cells. We now have grounds to question that assumption."10 Further evidence that ultrasound has an effect on cells is indicated in recent research that shows a higher-than-average rate of left-handedness in boys exposed to ultrasound in utero.11
THE TRIPLE SCREEN
This simple blood test measures the levels of three chemicals in the mother's blood: alpha-fetoprotein (AFP), and the hormones estriol and human chorionic gonadotropin (hCG). It does not identify the existence of any specific abnormality, only the presence of chemicals that can indicate risk.
Why Is the Triple Screen Used? The test is done to evaluate the risk of Down syndrome, spina bifida (a disorder where part of the spinal cord develops outside of the baby's body), anencephaly (where the skull fails to grow over the brain), and other abnormalities. If a fetus has Down syndrome, for example, the hCG levels in the mother's blood are often higher than normal, while estriol and AFP are often lower.12 High levels of AFP, on the other hand, may indicate risk of a neural tube defect such as spina bifida or anencephaly.13 These levels are factored in with a woman's age to calculate the likelihood that one of these abnormalities may be present.
How Is the Triple Screen Done? If you have this test, you will have blood drawn either in your practitioner's office or in a lab, around week 16. Results are usually available within a couple of days. Generally, if a woman receives a result indicating risk, she will be advised to take the test again. If she receives a second result indicating risk, further testing, such as ultrasound and amniocentesis, will be recommended, as will genetic counseling.
When Is the Triple Screen Necessary? The triple screen is an elective test. Some women over 40 who are pregnant with their first child find it reassuring, but it is not medically necessary.
When is the Triple Screen Unnecessary? The triple screen is not necessary during pregnancy, but it has been used routinely, up until recently, for women under age 35, while amniocentesis (described later in this section) has been routinely administered to women over 35. ACOG now recommends the triple screen for all pregnant women, since amniocentesis can cause miscarriage. It is not medically necessary, however, that you receive this test.
How Effective Is the Triple Screen? Because this test does not identify the existence of any specific abnormality, but only the presence of chemicals that may indicate risk, its results are inconclusive and open to interpretation. For example, while high levels of AFP are associated with spina bifida, they might also indicate the presence of more than one fetus. Low levels associated with risk of Down syndrome can simply mean that the fetus is younger than was previously thought.
Is the Triple Screen Safe? The triple screen is safe. It is a simple blood test. Although it is the least invasive of all prenatal tests, the triple screen has a high rate of false positives, which incorrectly indicate risk in healthy pregnancies, resulting in weeks of anxiety while further tests are evaluated. In fact, 96 to 98 percent of women who first receive a positive triple screen result will go on to have normal babies. The risk of this test is emotional rather than physical.
Amniocentesis is a procedure in which some of the amniotic fluid surrounding the baby is removed from the mother's uterus. The amniotic fluid has passed in and out of the baby's body, and therefore contains some of the baby's cells. These cells can be read to see if a disease such as Down syndrome, spina bifida, cystic fibrosis, Tay-Sachs, sickle-cell anemia, or anencephaly is present.
Why Is Amniocentesis Used? This test is used to obtain information about the baby's genetic makeup and the potential for genetically inherited diseases. It can also determine the gender of the baby. In addition, if there are concerns that the baby will be born prematurely, amniocentesis can determine if the baby's lungs are mature enough to breathe normally after birth.
How Is Amniocentesis Done? A hollow needle is inserted into the mother's uterus through her abdomen. A local anesthetic may be used, though discomfort might still be experienced. Ultrasound is conducted before the amniocentesis to determine the position of the baby and the placenta, to avoid hitting them with the needle. About half an ounce of amniotic fluid is removed for study. This test should take less than 30 minutes.
If you decide to have amniocentesis, you will need to take the day off. It is done either in a doctor's office or in a hospital. You will probably be advised to lie down at home after the test and rest. Some practitioners suggest their patients have a glass of wine to relax and reduce cramping. You will get results from the test in about two to three weeks. Your practitioner will not reveal the baby's sex to you unless you specifically ask for this information.
When Is Amniocentesis Necessary? As mentioned earlier, ACOG now recommends the less invasive triple screen in all pregnancies for women over 35, following up with amniocentesis only if high risk is indicated.
When Is Amniocentesis Unnecessary? Genetic conditions happen to the babies of women of all ages, while genetic accidents, such as Down syndrome, occur more often in the children of older mothers. This is one reason amniocentesis was routinely prescribed for women over 35, until recently. It may be, however, that other age-related factors, such as diet, general health, exercise, and exposure to radiation and environmental toxins-rather than age alone-are the real causes of genetic anomalies. That's why age alone is not an absolute indicator of risk.14 You can review questions regarding your own personal risks with your birth attendant.
How Effective Is Amniocentesis? While amniocentesis can diagnose hundreds of diseases and conditions, it is most effective when the laboratory is instructed to look for a specific condition. The procedure has two major disadvantages in terms of acting on the information. It can take two to three weeks for the results to become available, and the procedure is not usually done until the end of the fourth month, when sufficient fluid for testing is available. Culture failure, which occurs in 2 percent of test samples, can require a repeat sample and therefore prolong final results until well past the middle of the pregnancy.
Is Amniocentesis Safe? Amniocentesis carries a miscarriage risk of 1 to 3 percent (almost three times the miscarriage rate in a pregnancy where amniocentesis has not been performed).15 With a more experienced practitioner, the risk may be slightly less. Studies also show a risk of low-birth-weight infants in about 0.5 percent of women who have undergone the test, and an increase in respiratory distress syndrome in their infants.16
Side effects of the procedure itself include cramping, bleeding, and leaking of amniotic fluid. These side effects may be quite minor, or severe. In addition, those women whose tests have to be readministered double their risk of miscarriage, from 3 to 6 percent.
CHORIONIC VILLUS SAMPLING (CVS)
A small sample of the chorion, the outer sac that surrounds the embryo during the first two months of pregnancy, is gathered along with the villi, hair-like tissues that protrude from the chorion. These are studied to assess the fetal chromosomes for genetic abnormalities.
Why Is CVS Used? CVS was originally developed to detect chromosomal abnormalities early, at around week ten, because amniocentesis can't be effectively done until week 16. This allows a woman to terminate her pregnancy much earlier if the test confirms the presence of a severe problem.
How Is CVS Done? This test is done in a hospital setting. You will lie down and have an ultrasound examination to locate the baby's position in your womb. Then a hollow needle will be inserted through your abdomen (or vagina) into your uterus to gather a sample from the embryonic sac. The test is sometimes painful, but takes less than 45 minutes. Results will be available in about ten days.
When Is CVS Necessary? This is an elective test and is not medically necessary. It is normally reserved for cases in which earlier knowledge is important to the patient and the practitioner due to a high genetic risk for certain diseases.
When Is CVS Unnecessary? Because of its risks, which are discussed below, CVS is not recommended for most pregnant women.
How Effective Is CVS? CVS sampling is not quite as accurate as amniocentesis in assessing the presence of Down syndrome, and is not capable of assessing the risk of neural tube defects such as spina bifida.
Is CVS Safe? Some studies show a miscarriage risk of 1 to 5 percent associated with CVS, much higher even than the rate of 1 to 3 percent for amniocentesis, and nearly six times the average miscarriage rate. If the needle is inserted through the abdomen (as is more common now) rather than through the vagina, the risk is reduced.
Other suspected problems associated with CVS include higher rates of preterm birth, limb, and facial deformities, cervical lacerations, and maternal infection. These are more likely to occur if the test is conducted before ten weeks. There are also higher rates of false positives and failed tests, where the procedures must be repeated, than in amniocentesis.
EMOTIONAL IMPACT OF PRENATAL TESTS
The emotional effects of these prenatal tests have not been well studied. This means you need to take responsibility for figuring this out for yourself and for your family.
One of the most obvious effects of all of this testing is that it serves to "medicalize" your pregnancy. Trying to turn a healthy pregnancy into a medical experience can cause unnecessary worry and a tendency to avoid bonding too soon with the developing baby until it is "certain" that everything is okay. Going through these tests can make it easy to forget that birth is a normal process and does not need to be frightening. And remember-none of these tests is foolproof.
In fact, being forced to worry about conditions that ultimately work themselves out (like early diagnosis of placenta previa, for example, picked up in a routine ultrasound) can have negative effects. It is hard to shake off the anxiety of wondering whether everything is okay. Waiting two weeks for the result of an amniocentesis can be very stressful, even if you have every reason to believe that you and your baby are healthy.
Parents who are especially jittery, and think they might feel better after having these tests, need to consider this information even more carefully. You might think that prenatal tests will provide you with a sense of security, but unless there is a true indication of high risk, these tests can be misleading. You can find security by discussing your concerns with your healthcare provider, who will take the time to listen and explain, and by talking with your partner, doula, or friend.
Many women have testing done even though they have no intention of terminating an abnormal pregnancy. This is often because of pressure from family and friends to "find out" if everything is OK, even though these tests offer no guarantees. It can take great courage to say no under pressure. Remember that having prenatal tests done just to appease your family or partner will have consequences for only you. You must carefully think through each step of this decision, and review the possible consequences of prenatal tests, before you decide if they are right for you.
1. B. G. Ewigman et al., "Effect of Prenatal Ultrasound Screening on Perinatal Outcome," New England Journal of Medicine 329, no. 12 (1993): 821-827.
2. ACOG Technical Bulletin 187 (December 1993).
3. O. R. Brand et al., "Specificity of Antenatal Ultrasound in the Yorkshire Region: A Prospective Study of 2261 Ultrasound Detected Anomalies," British Journal of Obstetrics and Gynaecology 101, no. 5 (1994): 392-397.
4. J. Cnattingius, "Screening for Intrauterine Growth Retardation" (PhD diss., Uppsala University, Sweden, 1984).
5. F. Y. Chan, "Limitations of Ultrasound" (paper presented at Perinatal Society of Australia and New Zealand First Annual Congress, Freemantle, 1997).
6. ACOG Technical Bulletin 187 (December 1993).
7. NIH, "Diagnostic Ultrasound Imaging in Pregnancy," Consensus Development Conference Statement 5, no. 1 (1984, Washington, DC).
8. World Health Organization, "Diagnostic Ultrasound in Pregnancy, WHO View on Routine Screening," Lancet 2 (1984): 361.
9. Murray Enkin et al., A Guide to Effective Care in Pregnancy and Childbirth (New York: Oxford University Press, 2000), 58.
10. Patrick Brennan et al., "Shadow of a Doubt," New Scientist 12, no. 1476 (June 10, 1999): 23.
11. Helle Kieler et al., "Sinistrality a Side Effect of Prenatal Sonography: A Comparative Study of Young Men," Epidemiology 12 (2001): 610-623.
12. ACOG, www.medem.com.
13. Sheila Kitzinger, The Complete Book of Pregnancy and Childbirth (New York: Knopf, 1996), 220-221.
14. See Note 12.
15. Enkin et al., A Guide to Effective Care, 6.
16. Ibid., 64.
Peggy O'Mara is Mothering's publisher and editor.