Maternal Serum Screening

Maternal Serum Screening for Down Syndrome, Trisomy 18, and Open Neural Tube Defects.

Dr. Lescale offers Maternal Serum Screening for Down syndrome, Trisomy 18, and Open Neural Tube defects. The screening is a noninvasive test performed between 15 and 18 weeks of pregnancy. Dr Lescale points out that it is important to remember a screening test does not provide a diagnosis. Some women may have an abnormal screening, but with follow up testing find their babies are normal. Because screening cannot detect all high-risk pregnancies some women with a normal screening may have babies with defects. Maternal Serum Screening measures three (AFP3) or four (AFP4) different hormones that have been produced by the baby's liver and the placenta. These hormones pass into the mother's blood stream in small amounts. Maternal Serum Screening measures these amounts and compares them to the average level for women in the same week of pregnancy. From this information, the chance of a baby having Trisomy 18, Down syndrome, or open neural tube defect (Spina Bifida) is calculated. The test is completed by analyzing a small amount of blood taken from the mother’s arm. Factors that influence the hormones found in the mother’s blood include: the number of weeks pregnant the women is when the test is performed; weight, race, and age; medications being taken; whether a close relative has Down syndrome or open neural defect; and single or twin pregnancies. Screening leads to the detection of approximately 80% of Down syndrome cases with the AFP4 test and 70% of Down syndrome cases with the AFP3 test. Both tests detect approximately 60-80% Trisomy 18 cases and 75% of open neural tube defects. Dr. Lescale reiterates that an abnormal result does not mean the baby definitely has a defect. The result means the risk is higher than average and further testing is indicated. Causes for an abnormal test include incorrect pregnancy dating and unidentified twins. If an ultrasound rules out these causes Dr. Lescale may recommend a more detailed ultrasound or an amniocentesis.

Approximately 1 in 800 babies is born with Down syndrome. A baby with Down syndrome has an extra chromosome at chromosome number 21. The condition causes physical and mental retardation. However the degree of retardation varies from severe to minimal. Women over age thirty-five or those with a previous child with Down syndrome have a greater risk of having a child affected with Down syndrome.

Trisomy 18 occurs in 1 out of 3000 live births. Trisomy 18 babies have an extra chromosome at chromosome number 18. This chromosomal disorder causes severe mental retardation and numerous birth defects. Only a few Trisomy 18 babies live past their first year.

Open neural tube defects happen when the brain or spine does not develop properly. There are two kinds of open neural tube defects - Spina Bifida and Anencephaly. Spina Bifida is an opening in the bones around the spinal cord. It usually involves the skin and tissues around the spinal cord. This can result in a range of outcomes for the baby. Usually there is some weakness or paralysis of the legs. There may also be problems with bowel and bladder control as well as other medical problems such as Hydrocephalus (an accumulation of fluid around the brain). In most cases Hydrocephalus can be treated, but the problem with the spinal cord cannot be fixed. There is no way to tell how serious the physical problems might be or whether or not the person will have mental disabilities. With anencephaly the brain and back of the baby's skull are incompletely formed. This condition is not compatible with life and babies who have Anencephaly are often stillborn or die shortly after birth. Open neural tube defects occur in 1 or 2 out of every 1,000 births.

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