If you start prenatal care early enough (in the 1st trimester), you will inevitably have to decide on whether you want to be tested for potential genetic problem such as Down syndrome (aka Trisomy 21) or other life-threatening genetic conditions. Terms such as non-invasive prenatal tests (aka NIPS), Integrative Screens and Alpha-Maternal Serum Testing will be hurled at you along with very specific time tables for getting these tests done. Ideally, you should receive extensive counseling so that you may make an informed decision but quite often this is not the case.
Knowing the difference between screening and diagnostic tests is a great way to begin your decision-making process. A screening test identifies potential problems and requires additional testing. A diagnostic test provides a definite answer. Diagnostic tests in the first trimester include chorionic villi sampling (aka CVS) and amniocentesis is usually done in the second trimester. Both of these tests are invasive and carry a small risk for miscarriages. Risk factors such as advanced maternal age (meaning greater than 35) also affect a pregnant woman’s decision because the risk for Down syndrome increases with age. The risk of having any type of genetic disorder is 1 in 190 for women age 35 and 1 in 65 for women age 40.
NIPS have gained in popularity over the past decade because they have a less than 2% false positive rate for detecting Down syndrome by the 10th week of pregnancy but this rate increases slightly for other lethal genetic problems such as trisomy 13 and 18. They work by measuring the amount of fetal DNA found in the mothers’ blood stream. This test does NOT test for open neural tube defects such as Spina Bifida.
The integrative screening test is also done in the first trimester by measuring four pregnancy hormones in the mother’s blood and requires an early ultrasound to measure the baby’s neck (aka “nuchal test”) to rule out Down syndrome and has a false positive rate of approximately 5%. It also requires a second trimester Maternal Serum Alpha Fetal Protein test to rule out open neural tube defects.
The NIPS tests are not cheap, require insurance coverage and costs between $800 to $2700. They also cannot determine future heart problems, whether you’re having twins or other fetal abnormalities. But again, they are the most accurate test regarding screening for Down syndrome.
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