Prenatal Screening and Testing
(Ivanhoe Newswire) — It goes without saying that every expectant parent wants one thing, and that is to have a healthy baby. Over the past few decades, prenatal technology has become increasingly sophisticated, allowing parents to “screen” their unborn children for possible birth defects. But prenatal screening can be a double-edged sword. While testing can help ease the mind and nerves of expectant families, it also raises a number of questions and issues.
“It can raise issues that one can’t anticipate before deciding to do a test, because we’re human and we can’t always predict how we’re going to respond,” says Carol Isaacson Barash, Ph.D., a Boston based genetics and ethics expert. “Getting a result that one didn’t anticipate — both positive and negative — can change the dynamics between a couple and a family.”
First, there is the decision of whether or not to even undergo prenatal testing. It can be an agonizing decision for parents who are in a high-risk category, such as those with a known hereditary disease in the family. Second, advance notice of a genetic disease or developmental complication forces parents to make a decision regarding the fate of their unborn child — a decision that is often made under duress and one where the choices may all be equally unsatisfactory.
Types of Tests
There are a wide variety of tests available, ranging from simple blood tests and non-invasive ultrasounds, to more aggressive and invasive techniques such as amniocentesis. The appropriateness of a particular test has much to do with an individual couple’s background, in addition to how much knowledge they wish to have about their unborn baby.
Most pregnant women will undergo at least one ultrasound or sonogram during their pregnancy. This is a simple and non-invasive technique, which uses sound waves to construct an image of the fetus’ shape and position in the uterus. Ultrasounds pose no risk to either mother or baby, and while they were once used only in high-risk pregnancies, they have become a routine part of prenatal care. An ultrasound can help determine fetal age, rate of growth, position, movement, and heart rate, as well as indicating multiple births and the amount of amniotic fluid in the uterus. It can also detect genetic defects, such as Down syndrome, structural problems such as spina bifida and anencephaly, and even problems like a congenital heart defect or a cleft lip.
A number of other tests are routinely performed as part of a prenatal care regimen. A blood test is normally done to determine the Rh factor. If a woman’s blood is Rh positive and her partner’s is Rh negative, she may develop antibodies that can be deadly to the growing fetus. Rh incompatibility can be treated prenatally.
Blood tests also are performed to check maternal iron levels (low levels can lead to anemia, jeopardizing the health of both mother and baby), along with tests for hepatitis B, syphilis, and HIV — all of which can affect the health of the growing fetus.
Urine and cervical testing also check for kidney infections, gestational diabetes, and infections which can cause birth defects and/or serious health risks to the fetus, such as chlamydia, gonorrhea, and Group B streptococcus infection.
While these tests are slightly more invasive than ultrasound, they cause very minimal discomfort and pose no risk to either mother or baby.
Alpha-fetoprotein (AFP) test
This is another simple blood test that is performed during the 16th to 18th week of pregnancy. The AFP test, also known as the triple screen or triple marker, measures levels of a protein produced by the fetus and two pregnancy-produced hormones in the mother’s blood. While it is not conclusive, varying amounts of the hormones may be a sign that the fetus has a disorder such as Down syndrome or spina bifida. An abnormal test is usually followed up by more specific and invasive techniques.
This is an invasive test, which poses a risk to the fetus. Generally performed at 16 weeks or later, amniocentesis is used to determine genetic defects in the baby. It can also reveal the baby’s sex, presence of infection, and fetal maturity.
The test is performed by inserting a long needle, via the woman’s abdomen and guided by ultrasound, into the uterus. A sample of amniotic fluid is removed, and then sent to a laboratory for analysis. While it is very accurate, it causes approximately one in 200 to 400 miscarriages. It also carries a risk of uterine infection of less than one in 1,000, which can also cause fetal loss. Amniocentesis is not routinely offered to pregnant women, but instead, is usually recommended if the mother is over 35, the AFP test was abnormal, there is a family history of genetic disorders, or if the couple already has a child with a chromosomal defect.
Chorionic Villus Sampling (CVS)
This is also an invasive test, which involves removing a small sample of the placenta for testing. A catheter or needle is inserted through the vagina, into the cervix, and threaded upward until it reaches the placenta. A tissue sample is then removed. Alternatively, a needle can be inserted into the mother’s abdomen, in much the same fashion as amniocentesis.
The advantage of CVS is that it can be performed sooner in the pregnancy, usually by the 10th to 12th week. This is particularly advantageous if the couple plans on terminating the pregnancy if defects are found, or at least, gives them a little more time for counseling and decision making. The downside is that it carries a higher risk of miscarriage than amniocentesis (about 1 percent), and CVS is unable to test for neural tube defects. Like amniocentesis, this test is not part of routine prenatal care and is offered to those deemed at a higher risk of birth defects.
Percutaneous Umbilical Cord Sampling
Fetal blood can be tested by withdrawing a small amount from the umbilical cord. As in amniocentesis, an ultrasound-aided needle is inserted through the mother’s abdomen, into the umbilical cord, and then a blood sample is taken. This can be performed from 18 weeks gestation onward, and the blood can be tested for genetic defects, as well as Rh factors. Test results are available more quickly than from an amniocentesis. The miscarriage rate is about 2 percent, and like other invasive procedures, also carries a risk of infection with resultant fetal loss.
Both CVS and amniocentesis have nearly a 100 percent accuracy level in testing for specific genetic defects. The AFP test, on the other hand, is not meant to be a diagnostic. It is a screening test, which can only indicate that there is a higher risk. If the result is abnormal, then it is up to the couple to decide if they wish to proceed with further evaluation. Approximately 100 of every 1,000 women who take AFP will get an abnormal result, and of those, only two or three will actually be carrying a fetus with a birth defect.
“Women do need to be aware that an abnormal AFP is not a cause for alarm,” says Donnica Moore, M.D., a leading women’s health specialist and advocate. “It has many false positive results.”
But while genetic tests have a very high level of accuracy, technology is only available to test for a small fraction of birth defects. There are over 4,000 genetic disorders, and current technology is only able to test for about 350 of them.
“Each specific test, even if it’s testing for the same thing, has its own specificity,” says Dr. Barash. “So if you’re testing for mutations, there are at least 900 of them and no single test is going to test for all of them. The tests are usually developed to test for the most common occurring mutations in the population, and it’s always possible that a test will not pick up a mutation that is associated with a condition.”
For the most part, tests strive for accuracy. Dr. Barash points out that it is to no one’s advantage to develop a test that is not accurate and that is of limited value. “But it is always important to put out the caveat and there is always the possibility that the test may be inaccurate.”
Researchers are currently working on developing new tests that may pick up more genetic defects. However, many disabilities are the result of factors such as environmental toxins, maternal illness, or oxygen deprivation at birth — which have nothing to do with genetics.
Study data differs on ultrasound accuracy. Some suggest that it may miss as much as half of all structural defects, while another study suggests that it is able to detect up to three-quarters of them. Besides missing defects, ultrasounds occasionally can suggest a birth defect when none exists, which occurs in approximately one in 1,000 low-risk women. An abnormal result is generally followed up with more specific testing.
Newer techniques, such as 4-D (four-dimensional), have greatly enhanced ultrasound ability to the point where the picture is almost as clear as a photograph. In addition, 4-D shows “live action,” which shows the baby moving in real time. Some major medical centers are now using 4-D, which greatly enhances the ability to pick up birth defects such as cardiac problems, as 4-D shows the fetal heart beating in real time.
Reproductive technology, such as in vitro fertilization, allows parents to choose an embryo that is free of an inherited disease. If cystic fibrosis runs in the family, for example, a couple may have several embryos prepared in-vitro, and then select only the ones who are free of disease for implantation
The Impact of Incorrect Results
“There are instances of false positives and false negatives, and the impact can range from trivial to catastrophic,” says Dr. Barash. “It can even involve the state, which may end up paying for the child’s care.”
In extreme cases, she points out, parents have sued for wrongful birth. “They did prenatal testing for the purpose of avoiding a disease or disabled child, and the test gave them a false result.”
At present, 27 states recognize the tort of wrongful birth. Three states also recognize wrongful life lawsuits, where the child is compensated for a lifetime of disability. Needless to say, wrongful birth and wrongful life lawsuits have raised much controversy across all sectors.
At the other extreme, it is conceivable that a healthy fetus could be terminated based on a false result. But in the majority of cases, it would be difficult to know if it really was a false negative, as most testing is on the molecular level, according to Dr. Barash, and would not be visibly evident in the aborted fetus.
For most couples, an incorrect result will fall in the middle range. If the result is false positive, then they will undoubtedly be relieved to have a healthy baby.
“And in the instance of a false negative,” says Dr. Barash, “It is also possible that once the child is born, they may have a change of heart about raising a disabled child. They may come to love their child and find that this experience has enriched their lives.”
What are the benefits of not having the tests?
It relieves the couple of having to make any immediate decisions, says Dr. Moore. “In prenatal testing, you have a very short time frame to make a decision — a small window of opportunity in which you have to make the decision and then act upon it. And then the decision you make is not reversible.”
Up until the past few decades, there was no such thing as prenatal testing. For ethical, philosophical or religious reasons, many couples eschew testing. Testing can also be expensive if a women doesn’t have health insurance, and certain tests may not be covered by insurance.
And there are options, even if an unexpected disabled child is born, Dr. Barash points out. “If you feel that you can’t raise your child, you can put the child up for adoption.”
What are the benefits of having testing done?
“The advantage is that you can prevent a birth that you may not be able to cope with, or be prepared for the birth of a special needs child, ” says Dr. Barash.
Even if terminating a pregnancy is not an option, the knowledge that a condition exists will allow the couple to prepare for it, and educate themselves about the disability or disorder. Prenatal testing can help women manage the remaining weeks of the pregnancy, plan for possible complications with the birth process, and uncover conditions that may affect future pregnancies.