Inhibin A

Where it comes from

Made in

Granulosa cells of the dominant follicle, the corpus luteum, and the placenta

Sent out by

Peaks at mid-cycle and in the luteal phase; high through pregnancy

Acts on

• Pituitary gonadotrophs (FSH)
• Ovary (local)

What it does

• Shuts off FSH once a follicle has been chosen, so only one ovulates
• Its fall is one of the earliest signs of reproductive ageing, before FSH rises ¹
• A readout of corpus luteum and placenta rather than a target for treatment

In medicine

• The fourth marker of the second-trimester quadruple screen, where it is raised in Down syndrome; the four markers together found 81 per cent of cases at a 5 per cent false-positive rate ²
• A tumour marker for granulosa cell tumours of the ovary: in the first series, it was already raised 5 and 20 months before a recurrence showed itself ³
• Low in early pregnancy failure, alongside hCG and progesterone

Beyond the body’s own use

• Nothing is given as inhibin A and nothing blocks it in particular. The activin traps approved for anaemia and for pulmonary hypertension work on the other side of the same system
• Its screening job is being displaced by cell-free DNA testing, which reads fetal chromosomes directly, so the quadruple screen is now the second line where DNA testing is not available