Preterm labour is when women go into labour before 37 weeks' gestation. Babies born before term (preterm birth) have poorer outcomes compared with babies who are born at term. The earlier the baby is born, the poorer the outcome. Most preterm births occur in low-income countries where medical help is less readily available. Preterm birth is a major cause of infant deaths and serious illness worldwide. Preterm birth can result in respiratory distress syndrome and chronic lung disease, bleeding into the fluid spaces (ventricles) within the brain (intraventricular haemorrhage)), generalised infection or infection of the blood stream (sepsis), cerebral palsy and other neuro-developmental impairments. Even short delays in preterm birth can enable women to reach specialist care and receive 'corticosteroid' drugs that are given to women before birth to improve their babies' lung function.
We assessed the benefits of betamimetics (drugs that inhibit contractions of the uterus) given to women with preterm labour against any adverse effects in randomised controlled trials. The betamimetics were administered, by any route or any dose, and compared with placebo, no treatment or other betamimetics. Twenty trials, testing the effect of betamimetics for inhibiting preterm labour, contributed data.The trials were published over a 44-year period between 1966 and 2010 and were conducted in tertiary care or university hospitals in high-income countries.
A total of 1367 women in preterm labour participated in the 12 trials that compared a betamimetic with placebo or no treatment. Betamimetics decreased the number of women giving birth within 48 hours and there was a decrease in the number of births within seven days.
The delay in the timing of birth did not translate into any improvements in neonatal outcomes but most women in the trials were 32 weeks' gestation or more. Betamimetics were not shown to reduce perinatal deaths or respiratory distress syndrome.
The side effects for the woman were considerable. These led to cessation of treatment and symptoms such as palpitations, chest pain, headache, difficulty breathing, nausea and/or vomiting.
There was not enough evidence from the included trials to suggest that one betamimetic agent was superior to another.