Knowing What to Expect: Prenatal Testing for Down Syndrome

By Sarah V.

It is the most common chromosomal condition. All children have a chance of being born with it. All people with it are affected by it for their entire life. One out of every 691 babies in the United States is born with trisomy 21, commonly known as Down syndrome, making it a very present part of our society (“Down Syndrome Facts”). Down syndrome is caused by a full or partial extra copy of chromosome 21 which causes the affected child to experience cognitive delays and possibly some serious physical health problems. Now, a new, non-invasive diagnostic blood test has been developed for expecting mothers that tests their child for Down syndrome, allowing them to prepare for their child’s birth and life onward (“Down syndrome”).

Women who are over thirty-five years of age, have a family history of genetic disorders, or had a previous abnormal pregnancy are at a higher risk of having a child with Down syndrome (“Common Tests”). However, all women have the chance of having a child with Down syndrome. As a result, it has become routine for doctors to use non-invasive screening tests to identify if the baby is at risk of having Down syndrome. Currently, two options that many women choose during the first trimester are an ultrasound and blood tests. During the ultrasound, the doctor conducts a nuchal translucency screening test where they measure a region on the back of the baby’s neck to look for an increased amount of fluid which typically indicates an abnormality (“Down syndrome”). The screening blood tests check certain proteins and hormones found during early pregnancy. The first trimester blood tests check for abnormal levels of pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG) (“Common Tests”). During the second trimester, blood tests can also check for abnormal levels of alpha-fetoprotein, estriol, and inhibin (“Common Tests”).

While the screening tests cause no harm to the child, they are not conclusive and are often inaccurate on whether or not a fetus has Down syndrome. They have false positive rates of approximately five percent and fail to detect up to twenty percent of fetuses with Down syndrome (Song, Musci, and Caughey 1). If the fetus has the risk of having an abnormality, the mother is offered the option of having a diagnostic test performed. Older and more widely practiced diagnostic tests include amniocentesis, chorionic villus sampling (CVS), and percutaneous umbilical blood sampling (PUBS). These tests insert a needle into the mother’s uterus to take samples for testing. Despite their benefits, they each have a risk of terminating the pregnancy if the needle injuries the fetus or causes an infection. Amniocentesis is the most generally used and least risky test and is usually performed after the fifteenth week of pregnancy. During the test, a sample of the amniotic fluid surrounding the fetus is extracted and examined for the extra chromosome 21. However, amniocentesis carries a one in two hundred risk of causing a miscarriage. CVS can be done earlier in the pregnancy, between the ninth and fourteenth week. In CVS, a sample of fluid is taken from the placenta and then examined. However, this test has a one in one hundred risk of miscarriage. PUBS is typically only done when other tests have unclear results. During the test, blood is extracted from a vein in the umbilical cord, which is then analyzed. PUBS is generally done after eighteen weeks of pregnancy and “carries a greater risk of miscarriage than does amniocentesis or chorionic villus sampling” (“Down syndrome”). Along with testing for Down syndrome, these tests are able to also check to see if the baby has other genetic defects and disorders.

Many women decide against these invasive procedures because of the risks to the child (Bernhard). However, a new diagnostic test that is under study, known as non-invasive prenatal testing (NIPT), would eliminate the risk of a miscarriage caused by the tests. NIPT examines a sample of the mother’s blood for DNA from fetal cells that had traveled through the placenta from the child to the mother (Reardon). NIPT is “expected to further reduce the number of women who undergo [invasive diagnostic tests] to confirm a Down syndrome diagnosis” (Bernhard). Because it is non-invasive, there is no risk of causing a miscarriage. It can be done at about the tenth week of pregnancy and claims to have lower error rates than the older tests (Reardon). According to multiple studies, NIPT’s detection rates are more than 99 percent with missing up to one in one hundred abnormal cases and false positive rates are less than 0.1 percent with one in about five hundred false positive cases (Song, Musci, and Caughey 1; Non-Invasive Prenatal Testing (NIPT) Factsheet). NIPT is also more cost-effective than the screening tests combined (Song, Musci, and Caughey 2). It can also look for abnormalities other than Down syndrome such as extra copies of chromosomes 13 with Patau syndrome, chromosome 18 with Edward’s syndrome, and the X and Y sex chromosomes such as Klinefelter syndrome and Turner’s syndrome (Reardon; “Human Chromosomal Disorders”). However, it cannot test for other abnormalities, such as cystic fibrosis and spina bifida (English; Bernhard). Despite its benefits, NIPT’s use is not widespread because most insurance companies do not pay for the procedure, considering it experimental because it is not being reviewed by FDA. Thus, most expecting parents must pay for the total cost of the procedure (English). However, NIPT is being offered by multiple genetic testing companies, including Sequenom of San Diego, Verinata of Redwood City, Ariosa Diagnostics of San Jose, and Natera of San Carlos (Reardon). “Professional societies are beginning to make statements about the use of NIPT” (“Non-Invasive Prenatal Testing (NIPT) Factsheet”). The International Society of Prenatal Diagnosis (ISPD) believes NIPT is helpful as a screening test, but should be confirmed with invasive testing. The National Society of Genetic Counselors supports the use of NIPT, but “urges that NIPT only be offered in the context of informed consent, education, and counseling by a qualified provider, such as a certified genetic counselor” (“Non-Invasive Prenatal Testing (NIPT) Factsheet”).

While NIPT provides many benefits for expecting mothers, many are opposed to its widespread use based on its moral implications. They are concerned that with earlier and more accurate testing, women will be more likely to terminate their pregnancy because of the perceived burdens of having a disabled child. “Studies have shown as many as nine out of [ten] pregnancies with a Down syndrome diagnosis end in abortion” (Bernhard). Those against NIPT argue that the “increased use of unnecessary tests will further perpetuate … ignorance and discrimination toward the disabled community” (Chipman 14) and will create a “smaller community with fewer resources” (Bernhard). They believe that the test will legitimize the social stigma against those disabled who can be seen as inferior or a burden to society (Chipman 16). Also, the diagnosis could change the perspective of the parents by making them “focus on the disability rather than the possibility of giving birth to a caring and loving child who will potentially develop their own personality and provide their own contributions to society” (Chipman 14). As a result, they advise NIPT only be used for high risk pregnancies and not for the general public. Others advocating for the widespread use of NIPT believe that it is only a safer alternative to tests that are already available and that it allows the expecting mother more time to make an informed decision (Bernhard). They have stated they do not expect a large impact on the birth rate for children with Down syndrome (Bernhard).

Mothers are naturally worried for their unborn child and want nothing but the best for it. As a result, they test their child in order to know how to care for it when it is born. With this new option, this can be done safely with high degree of accuracy and no risk of harming the child. While the test does have moral implications, its benefits outweigh its downfalls for women at a high risk of having a child with Down syndrome. However, only time will tell if NIPT will be used by the public.  

Work Cited

Bernhard, Blythe. “Down syndrome is focus of new blood test for pregnant women.” St. Louis Post-Dispatch (MO) 21 Nov. 2011: Newspaper Source Plus. Web. 4 Apr. 2013.

Chipman, Peter. “The Moral Implications of Prenatal Genetic Testing.” Penn Bioethics Journal 2.2 (2006): 13-16. Penn Bioethics Journal, Spring 2006. Web. 11 Apr. 2013.

“Common Tests During Pregnancy.” Lucile Packard Children’s Hospital at Stanford. Lucile Packard Children’s Hospital, n.d. Web. 04 Apr. 2013.

“Down Syndrome Facts.” NDSS. National Down Syndrome Society, n.d. Web. 03 Apr. 2013.

“Down Syndrome: Tests and Diagnosis.” Mayo Clinic. Mayo Foundation for Medical Education and Research, 07 Apr. 2011. Web. 03 Apr. 2013.

English, Taunya. “Docs Offer First Trimester Down Syndrome Test.” WHYY, 15 Aug. 2012. Web. 11 Apr. 2013.

“Human Chromosomal Disorders.” IUPUI Department of Biology. Indiana University-Purdue University Indianapolis, 30 Apr. 2003. Web. 10 Apr. 2013.

“Non-Invasive Prenatal Testing (NIPT) Factsheet.” Oregon Health & Science University. Oregon Health & Science University, n.d. Web. 11 Apr. 2013.

Reardon, Sara. “Mother's blood key to new Down's test.” New Scientist 214.2868 (2012): 10. Academic Search Complete. Web. 4 Apr. 2013.

Song, Ken, Thomas J. Musci, and Aaron B. Caughey. “Clinical utility and cost of non-invasive prenatal testing with cfDNA analysis in high-risk women based on a US population.” The Journal of Maternal-Fetal & Neonatal Medicine (n.d.): 1-6. Informa Healthcare, 6 Mar. 2013. Web. 10 Apr. 2013.

Return to Home Page

sarah.txt · Last modified: 2013/04/16 20:33 by svangiezen