Prenatal Testing: Making an Informed Choice
I'm an advocate of truly having your eyes opened and honestly appraising how much power you really have, not pretending that you will have as much power as you desire, just because you really want it. I think that's the essence of informed consent. - Gretchen Humphries
by Katharina Bishop
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In the course of her pregnancy journey, a pregnant woman will be offered a wide variety of medical tests. The terms for many of these, such as amniocentesis and sonogram, are well known amongst the general population, indicating that these prenatal tests, while originally created to test certain high-risk pregnancy situations, have become standard procedures.
Many pregnant women accept the tests offered to them, without being informed on the side effects, complications and implications of positive test results. It is generally felt that these tests can do no harm. However, some of them have never been rigorously studied for safety to mother and child, and may present physical risks to both. Moreover, prenatal tests may give rise to concerns and anxiety, the very emotions that expecting mothers had hoped to avoid by agreeing to them. Test results can be vague and, more importantly, they can be misleading.
Before any type of medical procedure is carried out, medical professionals are obligated to obtain the patient’s consent. It is important to distinguish between consent and informed consent. Informed consent can only be given when the patient fully understands what will happen to them and their unborn child before proceeding with any type of testing or treatment. Nowadays, many tests are prescribed by doctors who simply assume that their patients understand what the tests are meant to assess, as well as their risks to mother and baby.
Specifically, informed consent means a clear understanding of how the procedure is administered, and of the risks associated with it, full knowledge of the alternatives (is there another test or procedure that poses less risk?), careful consideration of the physical and emotional impacts, and the freedom to say no.
In order to give informed consent, it is important to understand the tests and procedures that are routinely administered during pregnancy. The most popular ones, ultrasound, the triple screen, amniocentesis, and chorionic villus sampling, are discussed below.
An ultrasound exam is a procedure that uses high-frequency sound waves to create a picture (sonogram) of the baby and placenta. Ultrasound is used for two purposes. It may be used in cases where the woman has a known medical condition, or where previous tests have indicated a risk. More often, however, ultrasound is performed as a routine procedure during pregnancy to screen for potential problems, even where the woman is not at any particular risk. Most ultrasound exams last only a few minutes. The procedure is painless for the mother, although the full bladder that is usually required may cause some discomfort. Further 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. In general, ultrasound is more accurate to explore a specific situation, such as a predicted miscarriage, than when used in a generalized, routine way.
Ultrasound is generally seen as very safe. However, The National Institutes of Health (USA) cautions against routine use of ultrasound, suggesting 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."(1) The World Health Organization (WHO) also 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."(2)
The Triple Screen
This blood test is usually carried out between the sixteenth and eighteenth week of pregnancy. It measures the levels of three chemicals in the mother's blood: hCG (human chorionic gonadotropin) and estriol, which are produced by the placenta, and alpha-fetoprotein (AFP), which is produced by the fetus. It does not identify the existence of any specific abnormality, only the presence of chemicals that are indicators of a risk. 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 instance, the hCG levels in the mother's blood are often higher than normal, while estriol and AFP levels are often lower. High levels of AFP, on the other hand, may indicate risk of a neural tube defect such as spina bifida or anencephaly. Factors such as the mother's age, weight, and ethnicity, whether she is diabetic, if she is having twins or other multiples and the gestational age of the fetus all influence the levels of the substances being measured and need to be taken into account in interpreting the test result. 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, along with genetic counseling.
The triple screen is an elective test. It is not medically necessary. It is important to consider that this test does not identify the existence of any specific abnormality, but only the presence of chemicals that may indicate risk. Test results are thus inconclusive and open to interpretation. For instance, while high levels of AFP are associated with spina bifida, they may also indicate the presence of more than one fetus. Low AFP levels associated with risk of Down syndrome can simply mean that the fetus is younger than was previously thought. The triple screen test is the least invasive of all prenatal tests, but it has a high rate of false positives, which incorrectly indicate risk in healthy pregnancies, resulting in weeks of anxiety while further tests are evaluated. Between 96 and 98 percent of women who first receive a positive triple screen result will go on to have normal babies, making the risks of this test emotional rather than physical.
During this procedure a thin, hollow needle is inserted into the mother's uterus through her abdomen and a small amount of amniotic fluid (the fluid that surrounds the fetus) is removed and tested. The amniotic fluid has passed in and out of the fetus’ body, and therefore contains some of the baby's cells. These cells are used to obtain information about the baby's genetic makeup and the potential for genetically inherited diseases. Conditions tested for include Down syndrome, spina bifida, cystic fibrosis, Tay-Sachs, sickle-cell anemia, and anencephaly. 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. Side effects of the procedure itself include cramping, bleeding, and leaking of amniotic fluid. These side effects may be minor, or severe. Women whose tests have to be re-administered double their risk of miscarriage, from 3 to 6 percent.
Before agreeing to this procedure, it is very important to consider the implications of a positive test result. For women who feel the need to emotionally prepare themselves for a sick, disabled, or dying newborn, amniocentesis may be a useful test. Amniocentesis is also performed for women who consider terminating a pregnancy with a serious birth defect. Mothers who feel that amniocentesis results won't change their intention to carry a pregnancy to term or to parent a child with a birth defect may wish to consider not taking the risks associated with this test.
Chorionic Villus Sampling (CVS)
Using ultrasound as a guide, a thin tube is inserted through the vagina and cervix and a tiny tissue sample from 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 then studied to assess the fetal chromosomes for genetic abnormalities. CVS is usually performed around the tenth week. It is an elective test and is not medically necessary. CVS is generally reserved for cases in which earlier knowledge is important to the mother due to a high genetic risk for certain diseases. It is not as accurate as amniocentesis in assessing the presence of Down syndrome, and it is not capable of assessing the risk of neural tube defects such as spina bifida.
CVS carries a miscarriage risk of 1 to 5 percent, a higher rate than amniocentesis, and nearly six times the average miscarriage rate. The risk is lower when inserting the needle through the abdomen (as is more common now) rather than through the vagina. Other suspected complications associated with CVS include higher rates of preterm birth, limb and facial deformities, cervical lacerations, and maternal infection. Problems are more likely to occur if the test is carried out before ten weeks. CVS has higher rates of false positives and failed tests, where the procedures have to be repeated, than amniocentesis.
Making an Informed Choice
Prenatal tests, especially if administered routinely and frequently, serve to ‘medicalize’ a pregnancy. By transforming a healthy pregnancy into a medical experience, tests can cause unnecessary worry and stress. Parents may not permit themselves to bond with their developing baby until test results have ‘proven’ that everything is okay. Mothers who are especially nervous and seek reassurance by having these tests may want to take into account that test results can be misleading unless there is a true indication of high risk. In order to make an informed choice it is important to reflect on each step of the decision, and review the possible consequences of prenatal tests. It may prove helpful to discuss any concerns with a sympathetic doctor or midwife before making a decision that is right for you.
1. NIH, "Diagnostic Ultrasound Imaging in Pregnancy," Consensus Development Conference Statement 5, no. 1 (1984, Washington, DC).
2. World Health Organization, "Diagnostic Ultrasound in Pregnancy, WHO View on
Routine Screening," Lancet 2 (1984): 361.