Progesterone.

Progestogens are a promising treatment in the prevention of spontaneous preterm birth in high-risk women. In women with a prior history of spontaneous preterm delivery and in women with a sonographic shortened cervix, there is considerable evidence supporting a benefit of progestogen therapy in the reduction of preterm delivery. In women with multifetal gestations, progestogen therapy has not been shown to be beneficial. Data are inconclusive in women with arrested preterm labor. Questions remain about the mechanism of progestogen action, the optimal type of progestogen, the best mode of administration, and the ideal dosing regimen.