Potential methods for the prevention of preterm delivery include bed rest, cervical cerclage and prophylactic administration of progesterone. The prophylactic administration of progesterone beginning in mid-gestation to women who previously had a premature birth and in those with a short cervix has been shown to reduce the rate of spontaneous preterm birth before 34 weeks. On the other hand, randomized studies reported that, in twin pregnancies, bed rest was associated with a significant increase, rather than decrease, in the rate of early preterm delivery.