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by Nancy Sullivan, CNM, MS, FACNM
Q. I heard there is a new screen that's more accurate than the normal triple screen or AFP. I asked my midwife about it, and she said she wasn't aware of new tests, that the lab is good at notifying her of new tests. Do you have any information on this?
A. The quad test is "an enhanced prenatal screening test" for Down Syndrome, trisomy 18, and neural tube defects. It is done between the 15th and 20th week of pregnancy and measures substances that come from the developing fetus and placenta and are present in the mother's blood. The substances measured are alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), estriol (a form of estrogen) and inhibin-A. The last one, inhibin-A, is what makes this test "enhanced," since the routine triple screen does not include it.
This test is a screening test, meaning that a positive result places you in a higher risk group for having a baby with a problem, but does NOT diagnose a baby with such a problem. If the screening test is positive, other tests are recommended to check further. The most likely reason for an abnormal screening test is incorrect dating for the pregnancy. If you screen negative, it does not mean that you have no possibility of an affected baby, but does mean that you are at low risk: 1 in 1000 or less for neural tube defects, and less than a 35-year-old woman for Down Syndrome.
This new test is not yet available everywhere, and I am not sure how much "better" it is than the standard triple screen.
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