What if the results indicate that my baby is at high risk for a problem?Ī genetic counselor or maternal-fetal medicine specialist can help you understand your results and your options. This may cause you to undergo further testing and to worry about your baby's well-being unnecessarily. That is, it may identify your baby as being at high risk for one of these three problems when she is fine. On the other hand, this test has a 5 percent false positive rate. (While the test will pick up 81 percent of Down syndrome cases, for example, that means there's a 19 percent chance the test will miss the Down syndrome in a baby that has it.) This is called a false negative result, a falsely reassuring result that might lead you to decide against diagnostic testing that would have revealed a problem. The quad screen doesn't pick up all cases of Down syndrome, trisomy 18, or neural tube defects, so it may identify your baby as being at low risk for these problems when she really is affected. It just means that 81 percent of babies who have Down syndrome will have screening results that are suspicious enough to recommend additional testing. This doesn't mean that a screen-positive baby has an 81 percent chance of having Down syndrome. For Down syndrome, the quad screen detects about 81 percent of affected babies. The quad screen detects at least 70 percent of babies with trisomy 18 and about 85 percent of those with neural tube defects.
The same holds true for an abnormal AFP result and neural tube defects. In fact, most screen-positive babies turn out not to have a problem. And an abnormal screening result ("screen positive") doesn't mean that your baby has a chromosomal problem – just that he's more likely than the average baby to have one. Remember that a normal screening result (also known as "screen negative") isn't a guarantee that your baby has normal chromosomes, but it does suggest that a problem is unlikely. So, a result of 1 in 1,200 would be considered normal because the risk that there's a problem is lower than 1 in 250, and 1 in 100 would be considered abnormal because that risk is higher than 1 in 250. For example, some genetic screening tests use a cutoff of 1 in 250. You may also be told that your results are "normal" or "abnormal" for a particular condition, depending on whether the ratio is below or above a certain cutoff. If you're having the quad screen as part of an integrated or sequential screening, the results will be combined with those from the tests you took in your first trimester for a more comprehensive risk assessment and a higher detection rate.
To determine your baby's chances of having a neural tube defect, your level of AFP is plugged into a formula along with your age, your baby's gestational age, and other factors. For example, your likelihood of carrying a baby with Down syndrome ranges from about 1 in 1,200 at age 25 to about 1 in 100 at age 40.
Your age is factored in because although anyone can have a baby with a chromosomal abnormality, the risk increases as you age. To determine your baby's chances of having Down syndrome or trisomy 18, your levels of the four substances are plugged into a formula along with your baby's gestational age and your age. Low levels of the first three means your baby has a higher than normal risk of having trisomy 18 (Edwards syndrome). Low AFP, low estriol, high hCG, and high inhibin A are associated with a higher risk for Down syndrome. And in some cases, it doesn't mean any of those things. In rare cases, it can also signify a problem with the baby's kidneys. But in some cases, it's a sign of an abnormal opening in the baby's spine (spina bifida), head, or abdominal wall that's allowing AFP to leak out. If there's more AFP than expected, it may mean that you're carrying more than one baby or that your baby is older than your practitioner thought. A baby produces AFP throughout gestation, and a certain amount of it should cross the placenta into the mother's bloodstream at each stage. Inhibin A, a hormone produced by the placenta.Unconjugated estriol (uE3), a hormone produced by the placenta and the baby.Human chorionic gonadotropin (hCG), a hormone made by the placenta.Alpha-fetoprotein (AFP), a protein made by the baby.The test measures the levels of four substances in your blood: Results are usually available in about a week. You'll have a blood sample taken and sent to a lab for analysis.
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