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Inhibins are glycoproteins which belong to the transforming growth factor beta family (TGF-ß), which contains more than 60 proteins as well as activins, which are structurally similar but differ in terms of function. Inhibins in women are formed in the ovarian granulosa cells, inhibin A is also produced during pregnancy by the yellow body and the placenta. Inhibins play an important role in the regulation of folliculogenesis and oocyte maturation. In males, inhibins are predominantly produced in the testicular Sertoli cells and in a smaller quantity also in the Leydig cells. Their synthesis is stimulated by the effects of androgens but is primarily regulated by spermatogenesis. Currently, it is also clear that the function of inhibins include a much broader spectrum of effects, which are not only related to the reproductive system. In pregnancy, the source of inhibin A is the yellow body and later the placenta. Inhibin (and also activin) have a paracrine and autocrine function in the human placenta and locally affect the production of hormones in the placenta, cellular immunity, cell growth and differentiation of the placenta and embryo. Placental cytotrophoblast and syncytiotrophoblast secrete inhibin A, which inhibits the placental secretion hCG and progesterone. In some cases, biochemical markers that are produced by the placenta during pregnancy are used as markers for Down syndrome screening. It has been discovered that an increase in the level of inhibin A is to some degree associated with the presence of Down syndrome and may be used in combination with other biochemical markers produced by the fetoplacental unit as a biochemical screening marker. [ABSTRACT FROM AUTHOR]