INHIBIN A

Inhibin A is a gonadal peptide hormone produced mainly by ovarian granulosa cells (and by the placenta in pregnancy, and Sertoli cells in males). It exerts negative feedback on the anterior pituitary to suppress follicle‑stimulating hormone (FSH), helping regulate folliculogenesis, the menstrual cycle, and spermatogenesis. Clinically, inhibin A is used as a biomarker in prenatal screening and some reproductive conditions.

Inhibin A is a hormone from ovarian granulosa cells and the placenta that suppresses FSH and reflects ovarian/placental function. In pregnancy, elevated maternal inhibin A in second‑trimester screening is associated with higher risk of Down syndrome. Abnormal levels can also occur with certain granulosa‑cell tumors or reproductive dysfunction, so results are interpreted alongside other clinical and laboratory findings.

Inhibin is a marker for ovarian sex cord–stromal tumors, especially granulosa cell tumors. Both inhibin A and B can be elevated, but inhibin B is more commonly used and often more sensitive for diagnosis and monitoring recurrence. These tests help follow treatment response and detect relapse, but are not primary screening tools for epithelial ovarian cancers.

Inhibin A levels in pregnancy are gestational‑age dependent and usually reported as multiples of the median (MoM). The accepted “normal” range is roughly 0.5–2.0 MoM, with about 1.0 MoM as the median. Absolute pg/mL reference values vary by lab and week of gestation; levels above ~2.0 MoM are considered elevated and prompt further assessment.

Low inhibin A can result from reduced ovarian function—poor ovarian reserve, premature ovarian insufficiency, or ovarian damage (surgery, chemotherapy/radiation). In pregnancy, low inhibin A may indicate placental dysfunction, increased risk of fetal growth restriction or preeclampsia, and is seen in some chromosomal abnormalities (for example, trisomy 18). Cycle phase, anovulation and certain endocrine disorders can also alter levels.

Elevated maternal inhibin A during pregnancy most commonly reflects placental overproduction or dysfunction. Causes include fetal chromosomal abnormalities (especially Down syndrome), preeclampsia and other hypertensive/placental disorders, multiple pregnancy, and gestational trophoblastic disease. Incorrect dating can also alter levels. Elevated inhibin A usually prompts further diagnostic testing (ultrasound, diagnostic genetic testing) to clarify the cause.