Among the many congenital abnormalities that can occur in pregnancy, Down Syndrome is the most commonly talked about, and so raises anxiety in most pregnant women. This condition is widely known because of the fact that Down Syndrome is the most common cause of genetic mental retardation. Interestingly, the risk of the baby having this syndrome increases with maternal age.
Down Syndrome occurs in 1 out of 700 live births, in all races and economic groups. The defect lies in the chromosomes (there are 23 pairs of chromosomes where the human genetic material is located), wherein there is an additional third copy of chromosome number 21. Hence, this genetic disorder is also called Trisomy 21.
Children with Down Syndrome have distinguishing physical attributes, so that they look almost similar to each other. Apart from mental retardation, they have mongoloid features characterized with flat face, low-bridged nose, small chin, wide-set eyes, low set ears, and broad short neck. If you look at their eyes very closely, they have speckled appearance (white dots) of the iris, called the brushfield spots. They have weak muscular tone and they exhibit only one crease in their hands, called the palmar or simian crease. Add to that, children with this syndrome suffer from congenital heart defects, gastrointestinal anomalies, and by the age 40, virtually all will develop Alzheimer Disease. They also have 15-20x increased risk for acute lymphoblastic leukemia.
One established fact about Down syndrome is its association with maternal age. As the woman ages, her risk of having a baby with Down Syndrome significantly increases. Statistics show that at the age of 30, there is a chance of 1 in 965 births, at age 35 it is 1 in 365 births, at age 40 it is 1 in 109 births, and at age 45 it is 1 in 32 births.
Fortunately, there are ways to diagnose Down Syndrome even before the baby is born. The tests can be categorically classified into two:
1. Screening tests which include ultrasound and blood tests. The goal of screening tests is to estimate the risk of the baby having the condition. Although these tests are not accurate enough to make a firm diagnosis of Down syndrome, these tests are fast, easy and risk-free.
• For ultrasound: The soft signs of Down syndrome are the lack of nasal bone and a collection of fluid at the back of the fetal neck (radiologically termed as “nuchal translucency”).
• For blood tests: A blood sample from the mother is checked for a combination of different markers unconjugated estriol (uE3), alpha-fetoprotein (AFP), and human chorionic gonadotropin (hCG) known as the “triple test”. Oftentimes, a fourth marker called inhibin A is added, making the “quadruple screen.” Low levels of AFP and estriol and high level of hCG, plus maternal age can estimate the risk of having a baby with Down Syndrome.
2. Diagnostic tests include amniocentesis, chorionic villous sampling, percutaneous umbilical blood sampling. These tests are highly invasive which requires an elaborate procedure, and tends to be more expensive. However, a positive result of any of these tests are accurate in diagnosing Down Syndrome.
It used to be that the methods available for detecting Down Syndrome are the diagnostic tests which carry considerable risk of miscarriages. Hence, despite its accuracy, it was not appropriate to test every pregnancy this way. Before, the recommendation was to test only those with strong family history of genetic disorders and advanced maternal age of 35 and beyond.
But new technology has improved over the years and with the breakthrough of the screening tests which are a lot safer and practical, the current recommendation of the American College of Obstetricians and Gynecologists is that every pregnant woman should be offered a choice of screening tests for this common birth defect, regardless of age. The best time to screen for Down syndrome according to research is during the first trimester of pregnancy, although combined measurements of the first and second trimester also work well. If the screening test turns out to be positive, it means that the risk of having a baby with Down syndrome is higher. This then makes the woman a candidate for further diagnostic testing which can accurately tell if the baby indeed has the syndrome. A woman can also skip the screening test and go straight to invasive diagnostic testing, especially if chromosomal defects run in the family.
In conclusion, the decision to submit to the above test is all up to you. It is not compulsory to screen every pregnancy for Down syndrome. But if you wish to, consult your health care provider about this. Your doctor can help you understand more regarding Down syndrome and the implications of getting tested.