Advances in medical technology mean that pregnant women can choose to have tests during pregnancy to predict whether the fetus has characteristics that suggest abnormalities. Although birth defects are rare, the most common of those that do occur are the chromosome disorders Trimosies 13, 18, and 21, commonly known as Patau Syndrome, Edward Syndrome and Down Syndrome respectively (SOFT – Support Organization for Trisomy 18, 13 and related disorders) (n.d.). Statistically, the occurrence of any of those syndromes is as follows:
- Patau Syndrome (Trimosy 13): 1 in 10,000 live births; (SOFT – Support Organization for Trisomy 18, 13 and related disorders) (n.d.);
- Edward Syndrome (Trimosy 18): 1 in 7,000 live births (SOFT – Support Organization for Trisomy 18, 13 and related disorders) (n.d.);
- Down Syndrome (Trimosy 21): 9.2 per 10,000 live births (Newberger, 2000).
Note that although Trimosy 21 has the highest probability of occurrence, it is primarily a risk for women who become pregnant after the age of 30 – the older the woman from that age onwards, the greater the risk.
Because the likelihood of the occurrence of these disorders (even Trimosy 21) is relatively rare, and because there are other arguments against prenatal genetic testing, including the risk to mother and/or unborn child, causing unnecessary anxiety, and the costs of the tests, it is recommended that (e.g.) terminating a pregnancy on the basis of prenatal genetic testing results should be avoided unless absolutely necessary.
The Tests and the Risks
Kartha (May 2010) reported that genetic testing including prenatal genetic testing is a relatively recent development, typically considered by pregnant women to check if the baby they are carrying is free of genetic disorders. The most likely candidates for testing are women whose families have a history of genetic disease, women who have children with genetic defects, those who have had previous miscarriages, or pregnant women over 35. The latter group is known to have higher risk of giving birth to a child with genetic abnormality. Women in none of these categories have a much lower risk of birth defect problems.
According to Kartha, the tests can be divided into two types:
- “Maternal serum screening”: A sample of the mother’s blood is checked for possible birth defect characteristics. However, this test can indicate only a low or high risk of such problems, it cannot provide a definitive prediction. If the result shows high risk, the mother could choose to have the second test type:
- “Amniocentesis”: This test requires extracting and testing a sample of the “amniotic fluid” from the womb of the expectant mother. Results of these tests are reported to give accuracies as high as 98 percent.
Kartha stated that the arguments against undergoing prenatal genetic testing are that anxiety can result from the test outcomes, and that even if a test gives a positive result (i.e. presence of an abnormality) that does not mean the baby will definitely have the related defect; i.e. the accuracy is questionable. Further, that many believe that to terminate a pregnancy because the baby might develop a disorder is wrong. Also, the tests can be an unnecessarily expensive burden that insurance companies may well refuse to take on.
Kartha also stated that women can be tested even if their doctor does not suggest it. Then it is called Direct-To-Consumer (DTC) testing, which may not be such a good idea as – without the benefit of one’s own physician’s involvement – results could be misinterpreted.
Garvey (Sep 2012) also described prenatal genetic tests that an expectant mother can have, dividing them into three types:
- In the first trimester of pregnancy: blood sample and ultrasound test;
- “Quad screen” test in the second trimester: Tests blood sample for the presence of four substances to determine the risk factor;
- Combination of the two previous tests (“Integrated Screen”): More sensitive test said to provide better accuracy.
Garvey commented that whilst those tests are not dangerous, they can cause the mother-to-be “anxiety and emotional conflict.” She also cautioned that the tests cannot definitively confirm the presence of a defect, they can only indicate the possibility or probability. A test can miss signs of a defect, or sometimes can give a “false positive.”
Another type of test is called chorionic villus sampling (CVS) which can be performed between the 10th and 13th week of pregnancy, extracting cell samples from the placenta. It can be uncomfortable and cause subsequent cramps and does carry a slightly increased risk of miscarriage (Chorionic villus sampling, 2012).
Murry (Jan 2012) cautioned that women not in a high risk category, should give serious thought to whether any testing is right for them. It has to be an individual decision.
It is clear from the research that whilst prenatal genetic testing can be useful for women in certain higher risk categories, for most women it is not necessary, particularly because the likelihood of the baby actually being born with abnormalities is very low. Additionally, not only do certain invasive tests (chorionic villus sampling and amniocentesis) carry risks to the mother and/or unborn child, but many believe that to terminate a pregnancy because of the predicted possibility of birth defects is wrong, and further, that the testing costs are high and may not be covered by insurance.
Essentially, choosing to undergo prenatal genetic testing without known need (e.g. if not in a high risk category) is not only unnecessary and potentially expensive, but can carry added risks to both mother-to-be and the unborn child, so should be avoided.
Chorionic villus sampling. (2012). NHS choices. Retrieved from http://www.nhs.uk/conditions/Chorionic-Villus-sampling/Pages/Introduction.aspx
Garvey, Ellen. (Sep 2012). Pros And Cons Off Genetic Screening During Pregnancy. Health Matters Blog. Retrieved from http://www.bmhvt.org/healthmatters/pros-and-cons-of-genetic-screening-during-pregnancy
Kartha, Deepa. (May 2010). Prenatal Genetic Testing Pros and Cons. Buzzle. Retrieved from http://www.buzzle.com/articles/prenatal-genetic-testing-pros-and-cons.html
Murry, M., M. (Jan 2012). Prenatal genetic screening: Is it right for you? Mayo Clinic. Retrieved from http://www.mayoclinic.com/health/prenatal-genetic-screening/MY01966
Newberger, David, S. (Aug 2000). Down Syndrome: Prenatal Risk Assessment and Diagnosis. Am Fam Physician. 2000 Aug 15;62(4):825-832. Retrieved from http://www.aafp.org/afp/2000/0815/p825.html
Trisomy 18 Facts / Trisomy 13 Facts. (n.d.). SOFT – Support Organization for Trisomy 18, 13 and related disorders. Retrieved from http://trisomy.org/