Finding the right tests…
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Finding the right tests…
Hormonal
The triple marker test is a second-trimester pregnancy blood test, usually done between weeks 15 and 20, that measures three substances — AFP, hCG, and estriol. Along with your age and gestational week, the pattern of these results estimates the chance of Down syndrome, trisomy 18, or a neural tube defect such as spina bifida in the baby. It's the same idea as the quad screen but without the fourth marker, inhibin A, which makes it slightly less accurate at flagging Down syndrome. Like any screening test, an unusual result doesn't mean your baby has a condition — it means your doctor will likely suggest a detailed ultrasound or a more definitive test.
This test measures three substances in a blood sample taken from you during the second trimester — alpha-fetoprotein (AFP), hCG, and unconjugated estriol. As with the related quad screen, no single value is read as normal or abnormal alone; the lab combines all three levels with your age and gestational week to calculate a statistical risk score for your baby. Timing matters heavily, so the test is done in a fairly narrow window, usually 15 to 20 weeks, and accurate dating of your pregnancy affects how reliable the result is. No special preparation is needed for the blood draw.
AFP comes from your baby's liver, hCG from the placenta, and estriol from both the placenta and the baby together, and each normally follows a predictable pattern as pregnancy advances. Certain unusual combinations of these three levels are statistically linked to a higher chance of Down syndrome (trisomy 21), trisomy 18, or a neural tube defect such as spina bifida.
The triple marker test measures the same three substances as the quad screen but leaves out the fourth marker, inhibin A. Adding inhibin A makes the quad screen somewhat more accurate at flagging Down syndrome specifically, which is one reason many labs now default to the quad version — but the triple marker test remains in use and follows the same basic logic.
The lab reports a calculated risk, such as a 1-in-300 chance, not a yes-or-no diagnosis. An unusually high AFP alone, for instance, is more often linked to neural tube defects, while a pattern of low AFP, low estriol, and high hCG is more associated with Down syndrome risk. A result outside the expected range means your doctor will likely recommend a detailed ultrasound or offer a more definitive test, such as amniocentesis, rather than treating the screen itself as an answer. Most women with an unusual result still deliver a baby with no chromosomal condition.
The triple marker test measures AFP, hCG, and estriol, while the quad screen adds a fourth substance, inhibin A, which makes it somewhat more accurate at flagging Down syndrome risk. Both work on the same basic principle of calculating a statistical risk score.
No. This is a screening test, and an abnormal result means the statistical chance is higher than average, not that a condition is confirmed. Most women who get an abnormal result go on to have a baby with no chromosomal condition, and your doctor will discuss further testing.
It's usually done between 15 and 20 weeks of pregnancy, based on MedlinePlus guidance on second-trimester screening. Testing outside this window can affect how reliable the calculated risk 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.
An unusually high AFP level is more often linked to an increased risk of neural tube defects like spina bifida, or can reflect a multiple pregnancy or inaccurate dating, rather than Down syndrome specifically.
Your doctor will typically recommend 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'd like it.
The risk calculation depends heavily on how many weeks pregnant you are, so inaccurate dating can throw off the result. Your doctor will usually confirm dating with an ultrasound around the time of this test.