Babies who are born before 37 weeks, and particularly those born before 34 weeks, are at greater risk of having problems at birth and complications in infancy. Infants who are born preterm are at greater risk of dying in their first year of life, and of those infants who survive, there is an increased risk of repeated admission to hospital and adverse outcomes including cerebral palsy and long-term disability. Progesterone is a hormone that reduces contractions of the uterus and has an important role in maintaining pregnancy and is suggested for the prevention of preterm labour. Maternal side-effects from progesterone therapy include headache, breast tenderness, nausea, cough and local irritation if administered intramuscularly. At present, there is little information available regarding the optimal dose of progesterone, mode of administration, gestation to commence therapy, or duration of therapy.
The review of 36 randomised controlled trials, involving a total of 8523 women considered to be at increased risk of preterm birth, and 12,515 infants, found that where progesterone was given (by injection into the muscle in some studies and as a pessary into the vagina in others), it had beneficial effects, including reducing the risk of the baby dying after birth, suffering complications such as requiring assisted ventilation, necrotising enterocolitis or requiring admission to neonatal intensive care, prolonging the pregnancy, and reducing the chance of neonatal intensive care admission.
Information related to longer-term infant and childhood outcomes was limited. Overall, the trials included in this review were considered to be of good to fair quality. Further trials are required to assess the optimal timing, mode of administration and dose of administration of progesterone therapy.