Genetic Testing

In early pregnancy we are concerned about the baby’s health, and we perform frequent testing to check it. One of the areas that is tested has to do with genetics. According to the American Congress of Obstetricians and Gynecologists almost all children in the United States are born healthy. Only about 2 or 3 out of 100 newborns have major birth defects. For the majority of these the cause is unknown. However, there are certain birth defects that can be tested for prenatally- before the baby is born. These Include Down Syndrome, trisomy 18, trisomy 13, and open neural tube defects.

The risk of having a baby with a chromosome abnormality, such as Down syndrome, increases with the mother’s age. However, ACOG recommends prenatal testing be offered to all pregnant women, regardless of age.

About 5 years ago a new test was developed in England that soon became popular in the United States and around the world. The First Trimester Genetic Screening Test is a simple blood test performed on you with a finger stick combined with an ultrasound of the fetus when it is between 11 weeks and 14 weeks gestation. The ultrasound confirms your baby’s age and measures the amount of fluid behind the baby’s neck.

Results of the blood test and the ultrasound are combined to estimate the risk of Down syndrome, trisomy 18 and trisomy 13. 91% of Down syndrome cases are detected and 95% of trisomy 18 and trisomy 13 cases are detected.

This picture is an example of the test results. This example shows that the risk, age related, is estimated as relatively high before the test is done. The test result shows it to be lower than was expected.

If you are screened for chromosome abnormalities in the first trimester, you should also be tested for neural tube defects (such as Spina Bifida) in your second trimester. This is done by the serum AFP test in our office. It is routinely done between 15 and 19 weeks of gestation. High levels of AFP in the mother’s blood may indicate that the developing fetus has a neural tube disorder.

Most of the screening results will be negative. A negative First Trimester Genetic Screening Test means that your baby’s risk of Down syndrome is low. A negative test does not completely eliminate the possibility that your baby has Down syndrome, trisomy 18 or trisomy 13. If you want to have additional testing, it is available.

A positive screen occurs in about 5% of tests. When you receive a positive result we will discuss it. Usually further testing is recommended, such as chorionic villus sampling (CVS) or amniocentesis. These tests are associated with a small risk of miscarriage, so you should discuss it with us before proceeding. If you decide to have further testing, we usually will recommend a genetic specialist for it, where the risks of having the testing done are very low.

We are also pleased to offer new additional genetic carrier testing for Cystic Fibrosis, Spinal Muscular Atrophy, and Fragile X Syndrome. While much of our testing during pregnancy is performed to be sure that everything is progressing normally, some tests may be ordered to determine if you and your partner harbor genes that cause conditions that may affect this pregnancy, or a future one. This type of testing is called Carrier Testing.

Cystic Fibrosis (CF) is the most common fatal disorder in North America. It affects about 1 in 3,300 people in the U.S. It causes the body to produce abnormally thick mucus, leading to life threatening lung infections, digestive problems and poor growth. Symptoms of the disease range from mild to severe, and some individuals may reach adulthood without knowing they have the disease. It does not affect intelligence. The average life span for an individual with it is 37.

Spinal Muscular Atrophy (SMA) is the most common cause of infant death in children under the age of two. Every year about 1 in 6,000 to 1 in 10,000 babies is born with SMA. It is a sever, often fatal genetic disorder in which muscles needed for breathing become progressively weaker and waste away. THere is currently no treatment for it.

Fragile X Syndrome is the most common inherited cause of mental impairment. It affects approximately 1 in 4,000 males and 1 in 8,000 females. The spectrum ranges from learning disabilities to severe mental retardation. and autism.

Be sure to ask us questions about these tests to decide which are best for you.

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