Since the discovery of progesterone researchers have studied whether administration of exogenous progesterone can prevent preterm birth. Two trials were published in 2003 that showed a positive effect of progesterone with regard to the prevention of recurrent preterm birth. However, more recent data do not support these findings. In multiple pregnancies the use of progesterone does not seem to reduce the number of preterm births. The results in pregnant women with asymptomatic shortening of the cervix are promising, although more research is needed in this group.