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There are two types of prenatal Down syndrome screening tests. Screening tests can let you know if your baby does not have this chromosomal disorder, while later diagnostic tests can confirm that the fetus does, in fact, have Down syndrome. Generally screenings are done around 11 weeks and later tests, between the 15th and 20th week of gestation, are performed if there is reason to believe the baby may be at risk. Screening tests are very non-invasive and relatively painless. These Down syndrome screening procedures are primarily done to let parents know whether or not they want further testing done. One screening test for Down syndrome is called Nuchal translucency testing, which is performed between 11 and 14 weeks of pregnancy. Using ultrasound, doctors can measure the space in the folds of tissue behind a baby's neck where excess fluid typically accumulates for babies with Down syndrome. This procedure accurately predicts Down syndrome 80% of the time. Additionally, a blood test called "the triple screen" or "multiple marker test" is also performed at the 15-20 week mark. Doctors will check the blood for alpha fetoprotein plus, plasma protein-A and the hormone chorionic gondatropin. The second type of Down syndrome diagnostic tests are about 99% accurate in detecting signs of this chromosomal disorder. However, these procedures are more invasive and sometimes result in a miscarriage or other complications. Typically, doctors only perform these tests on women over 35, if genealogy warrants it or if they've tested positive in the initial screening. Amniocentesis, performed from 16 to 20 weeks, uses a needle to remove a small amount of amniotic fluid from the womb. While it's an out-patient treatment, women may experience cramping, bleeding and infection, not to mention that 2-3% of patients lose their baby. As a result, amniocentesis is not recommended before the 14th week of gestation. Chorionic villus sampling and percutaneous umbilical blood sampling are other alternatives. With chorionic villus sampling, a small sample of placenta is removed through a needle inserted into the abdomen. This Down syndrome screening can be done between the 10-12th weeks of gestation. Rate of miscarriage following the procedure is 3-5% and the use of CVS before the 10th week of pregnancy resulted in babies with missing or shortened fingers or toes. At the 20-week mark, percutaneous umbilical blood sampling (PUBS) can test for Down syndrome. A small sample of blood is removed from the umbilical cord and the risks are comparable to amniocentesis. Mike Selvon portal offers free articles on down syndrome. Find out more about down syndrome screening, and leave a comment at the down syndrome information blog.
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