Finding the right tests…
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Finding the right tests…
Hormonal
The quad screen is a blood test done partway through pregnancy, usually weeks 15 to 20, that measures four substances — AFP, hCG, estriol, and inhibin A. It doesn't test your baby directly; it uses the pattern of these four levels, with your age and how far along you are, to estimate the chance of Down syndrome, trisomy 18, or a neural tube defect such as spina bifida. This is a screening test, not a diagnosis — a result outside the usual range means your doctor will likely suggest an ultrasound or a more definitive test like amniocentesis, not that something is confirmed to be wrong. Most women with an unusual result go on to have a healthy baby.
This test measures four substances in a blood sample taken from you during the second trimester — AFP, hCG, unconjugated estriol, and inhibin A. None is measured against a single fixed range the way a blood sugar result is; instead, the lab combines all four levels with your age and gestational week to calculate a statistical risk score for your baby. Because timing matters so much, the test is done in a fairly narrow window, between about 15 and 22 weeks, and is most accurate at 16 to 18 weeks. No special preparation is needed for the draw itself.
Each of the four substances in this screen comes from the placenta or the developing baby and normally follows a predictable pattern as pregnancy progresses. Certain combinations of unusually high or low levels are statistically associated with a higher chance of Down syndrome (trisomy 21), trisomy 18, or a neural tube defect such as spina bifida.
The lab doesn't report a yes-or-no answer. It reports a risk estimate — for example, a 1-in-250 chance — calculated from your four hormone levels together with your age and gestational week. This is why accurate dating of the pregnancy matters so much to the result; being off by even a couple of weeks can shift the calculated risk.
A risk score outside the expected range does not mean your baby has a chromosomal condition. It means your doctor will likely recommend a detailed ultrasound to look for physical markers, and may offer a more definitive test such as amniocentesis or cell-free DNA screening to get a clearer answer. Most women who receive a high-risk result on this screen go on to have a baby with no chromosomal condition at all — screening tests like this one are built to flag possibilities for further checking, not to diagnose.
Quad refers to the four substances measured — AFP, hCG, estriol, and inhibin A — one more than the triple marker test, which measures the same three without inhibin A. Adding inhibin A makes this version somewhat more accurate at flagging Down syndrome risk.
No. A high-risk result means the statistical chance is higher than average, based on MedlinePlus guidance on quad screening, not that a chromosomal condition is confirmed. Most women who get a high-risk result go on to deliver a baby with no chromosomal condition, and your doctor will discuss further testing.
It's usually done between 15 and 22 weeks of pregnancy and is most accurate between 16 and 18 weeks, according to MedlinePlus. Testing outside this window can affect how reliable the result is.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Your doctor will likely suggest a detailed ultrasound to look for physical markers, and may offer amniocentesis or cell-free DNA testing for a more definitive answer, along with genetic counselling if you want it.
The risk calculation depends heavily on how far along your pregnancy is, so an inaccurate due date can throw off the result. Your doctor will usually confirm dating with an ultrasound before or around the time of this test.
No. This is a screening blood test that estimates risk and carries no risk to the pregnancy, while amniocentesis is a diagnostic procedure that samples amniotic fluid and can give a definitive answer, but carries a small risk of miscarriage.