The disclosure is directed to a method of enhancing progesterone receptor (PR) activity in a mammal, which comprises administering a composition comprising an inhibitor of FK506 binding protein 51 (FKBP51) to a mammal in need thereof, such as a pregnant human female, whereby progesterone receptor activity in the mammal is enhanced as compared to a mammal not administered the composition. The method results in an extension of the gestation period and a decreased likelihood of preterm birth and fetal growth restriction.