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ABNORMAL TRIPLE SCREEN: INCREASED RISK FOR DOWN SYNDROME The triple screen is a screening test used to detect women at increased risk for three types of problems in their pregnancies: open neural tube defects (such as spina bifida, an opening along the spine), trisomy 18, and Down syndrome (both of which are chromosome abnormalities). The triple screen measures the mother's blood for three pregnancy-related chemicals – AFP, estriol, and hCG – which should fall within a normal range. Pregnancies affected by Down syndrome are more likely to yield low levels of AFP and estriol, and a high hCG level. Down syndrome risk is calculated from the mother's age and the three values measured in the blood. Chromosomes are the inherited structures in the cells of our bodies. There are 46 chromosomes in each cell, arranged into 23 pairs. Chromosome abnormalities involving a missing or extra chromosome are not inherited or caused by an exposure during pregnancy. Instead, they result from a chance mistake in cell division at the time of conception. This error is a random event that can occur in anyone’s pregnancy. Individuals with Down syndrome have an extra #21 chromosome, thus three rather than two copies of chromosome 21. It is this extra genetic material that causes the features of Down syndrome, including mental retardation, a characteristic facial appearance, and other health problems. Since an abnormal triple screen may indicate an increased risk for Down syndrome or other abnormalities in the baby, there is the option for diagnostic testing by amniocentesis.
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