Inhibin A

Inhibin A is a hormone that can be detected in the mother’s blood especially in the second trimester, i.e. weeks 16-18. It is secreted by the foetus and the placenta in response to the follicle-stimulating hormone (FSH) to which inhibin A reacts with a negative feedback loop and subsequently suppresses expression of FSH. Elevated inhibin A concentrations in maternal blood in conjunction with other hormones in pregnancy may be a sign of Down syndrome (Chasen, 2014, Hill, 2020).