D-chiro-inositol is one of the nine stereoisomers of inositol, a water-soluble cyclic carbohydrate with six hydroxyl groups. Inositol has an essential function in the activation of crucial enzymes in glucose metabolism. In fact, D-chiro-inositol shortage can lead to insulin resistance development. D-chiro-inositol administration in pathologies where insulin resistance is an important factor, i.e. diabetes, has given satisfying results; however, in other disorders, i.e. Polycystic ovary syndrome, this stereoisomer can be detrimental for pregnancy. Indeed, high follicular D-chiro-inositol levels in the presence of reduced myo-inositol values are associated with worsened oocyte quality. In conclusion, some recent studies and researches suggest that restoring the physiologic ratio between myo-inositol and D-chiro-inositol is mandatory to protect the efficiency of the reproductive system in women.