Serum Screening Tests Now numerous serum screening tests (blood tests) are available during pregnancy that estimate your chance to have a baby with Down syndrome and other chromosome problems. While these tests vary as to when in pregnancy they are done, and their sensitivity (the likelihood that they give you a correct answer), they all measure substances that are made either by the fetus or the placenta. The main advantage to serum screening compared to diagnostic testing is that there is no risk of miscarriage associated with these serum screening tests. First Trimester Serum Screening Testing and Results During the first trimester, two substances -- free beta HcG and PAPP-A -- found in mom’s bloodstream, are measured and used to give a chance for the baby to have Down syndrome or trisomy 18. The chance estimate is based on the levels of these substances in your blood, your age, your weight and how far along you are in the pregnancy. Typically this blood test is done between 10 to 14 weeks of pregnancy. This test only screens for Down syndrome and trisomy 18. Results are reported as “screen negative” or “screen positive” and only give an estimate of your chance to have a fetus with a chromosome condition. Serum screening tests cannot diagnose Down syndrome and other chromosome abnormalities. “Screen negative” results mean that your chance to have a fetus with these disorders is low and no follow-up testing is offered. It is important to remember that a “screen negative” result does not guarantee that there are no birth defects. If you have a “screen negative” result, you will not be offered follow-up diagnostic testing such as CVS or amniocentesis. You will also be offered another serum screening test, done in the second trimester, that measures a substance called AFP. The amount of AFP present screens for open neural tube defects such as anencephaly and spina bifida. “Screen positive” results meaning that the chance for the fetus to have one of these chromosomal conditions is higher than usual and follow-up testing such as CVS or amniocentesis is offered. And a “screen positive” result does not mean that the baby has a birth defect. In fact, most women with “screen positive” results will have normal healthy babies.
Posted on: Fri, 02 May 2014 11:29:31 +0000
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