|What is Down Syndrome?|
Down syndrome (or Down’s syndrome) is a chromosomal disorder caused by an error in cell division that results in an extra 21st chromosome. The condition leads to impairments in both cognitive ability and physical growth that range from mild to moderate developmental disabilities. Through a series of screenings and tests, Down syndrome can be detected before and after a baby is born.
The only factor known to affect the probability of having a baby with Down syndrome is maternal age. That is, less than one in 1000 pregnancies for mothers less than 30 years of age results in a baby with Down syndrome. For mothers who are 44 years of age, about 1 in 35 pregnancies results in a baby with Down syndrome. Because younger women generally have more children, about 75% – 80% of children with Down syndrome are born to younger women.
|How is Down Syndrome Screened and Diagnosed?|
Some families have prenatal exams that indicate various possible problems, and others already know that they have an increased chance of having a child with Down syndrome. These families often receive screening and diagnostic tests for the condition. It is also standard for pregnant women older than 30 or 35 to receive genetic screens because the risk of having a child with Down syndrome is increased as women age.
Screening tests are used to estimate the risk that a fetus has Down syndrome and diagnostic tests can tell whether the fetus actually has the condition. Screening tests are a cost-effective and less invasive way to determine if more invasive diagnostic tests are needed. However, unlike diagnostic tests, screening tests cannot give definite answers as to whether the baby has Down syndrome. Diagnostic tests, which are 99% accurate in detecting Down syndrome and other problems, are usually performed inside the uterus and carry an extra risk of miscarriage, fetal injury or preterm labor.
Screening Test Include:
- Nuchal translucency testing (at 11 to 14 weeks)
- An ultrasound that measures clear space in folds of tissue behind the neck of a developing baby.
- Triple screen or quadruple screen (at 15 to 18 weeks)
- Measures the quantities of normal substances in the mother’s blood.
- Integrated screen
- Combines first trimester screening tests (with or without nuchal translucency) and blood tests with second trimester quadruple screen.
- Genetic ultrasound (at 18 to 20 weeks)
- Detailed ultrasound combined with blood test results.