Finding the right tests…
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Finding the right tests…
Hormonal
Inhibin A is a hormone made by the ovaries and the placenta during pregnancy, and it's one of four markers checked in the second-trimester quad screen for Down syndrome, usually done between 15 and 20 weeks. The other three are AFP, hCG, and estriol. In pregnancies with Down syndrome, inhibin A levels tend to run higher than expected for the stage of pregnancy. Like the first-trimester Dual Marker test, this is a screening test that estimates a chance, not a diagnosis. A higher-chance result means your doctor may suggest further testing, not that a condition is confirmed.
The test measures inhibin A in a blood sample, as one part of the quad screen alongside AFP, hCG, and estriol. The lab combines all four values with your age and stage of pregnancy to calculate a single Down syndrome risk figure. Including inhibin A alongside the other three markers is intended to improve how well the overall quad screen tells apart higher- and lower-chance pregnancies, compared with using three markers alone.
Inhibin A is a protein produced by the ovaries and, during pregnancy, by the placenta. In pregnancy screening, it's measured as one of four markers in the quad screen, done in the second trimester, generally between 15 and 20 weeks.
- Alpha-fetoprotein (AFP) - Human chorionic gonadotropin (hCG) - Estriol (a form of estrogen) - Inhibin A
Each marker tends to shift in a particular pattern in pregnancies affected by Down syndrome; for inhibin A, levels tend to run higher than expected. Your lab combines all four results with your age and pregnancy dating to produce a single risk estimate.
This test cannot confirm or rule out Down syndrome by itself. It estimates a chance, and adding inhibin A to the older three-marker test is intended to improve how well doctors can sort higher-chance from lower-chance pregnancies. A higher-chance result usually leads your doctor to suggest further testing, such as NIPT or a diagnostic procedure like amniocentesis, for a more definite answer. A lower-chance result makes Down syndrome less likely but doesn't rule it out completely.
Because inhibin A levels change through pregnancy, this test only works within its intended window. Ask your doctor or the centre to confirm the right timing for your dates.
No. It means your calculated chance is higher than average based on the quad screen, not that your baby has the condition. Your doctor will likely suggest further testing to get a clearer answer.
It's typically done as part of the quad screen between 15 and 20 weeks of pregnancy. Ask your doctor or the centre to confirm the right window for your dates.
Some women have first-trimester screening, second-trimester screening, or both, depending on when they start antenatal care and their doctor's advice. Discuss which option, or combination, makes sense for you.
No special fasting is usually required for this blood test. Confirm the details with your doctor or the centre when you book.
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.
A low-chance result makes Down syndrome less likely but doesn't rule it out completely. Your doctor will continue routine pregnancy care and scans as usual.
Adding inhibin A to the three original markers is intended to improve how accurately the test can tell apart higher- and lower-chance pregnancies, compared to using AFP, hCG, and estriol alone. That's why it's called the quad, rather than the triple, screen.
No, it's a blood test that's usually done alongside, not instead of, your routine pregnancy ultrasounds. Your doctor uses both together to assess your pregnancy.