Progesterone and preterm: seventy years of "déjà vu" or "still to be seen"?

Progestogens for the prevention of preterm birth have a long history. In 2003, two widely publicized double-blind trials, one of daily vaginal progesterone suppositories and the other of weekly intramuscular injections of 17alpha-hydroxyprogesterone, claimed that the treatments effectively reduce the incidence of preterm birth in women at risk of spontaneous preterm labor. Critical analysis of the reports provides no convincing evidence that either one of these treatments is worth pursuing outside the context of controlled research to determine, first, whether and, second, how the treatments might work.