Use of Beta Agonists in Preterm Labo

Clinical Question

Do betamimetics (i.e., beta agonists) improve outcomes for women with preterm labor?

Evidence-Based Answer

Treatment with betamimetics decreases the number of women with preterm labor who give birth within 48 hours, but it does not decrease the number of births within seven days. Limited evidence suggests that treatment with beta-mimetics does not decrease perinatal death or morbidity.

Practice Pointers

Betamimetics commonly are used to decrease uterine contractions in women with preterm labor. However, they may cause discomfort and life-threatening adverse effects such as pulmonary edema and hypokalemia. Anotayanonth and colleagues identified 11 randomized controlled trials of betamimetics in 1,332 women with preterm labor.

Compared with placebo, the betamimetic ritodrine significantly decreased the number of women who give birth within 48 hours (23 versus 39 percent; relative risk [RR], 0.63; 95 percent confidence interval [CI], 0.53 to 0.75). This corresponds to a number needed to treat of 6. It also reduced the risk of delivery within seven days. This benefit did not persist after the authors performed a sensitivity analysis with a random-effects model.

Most of the participants were at 32 weeks’ gestation or more. Maternal adverse effects included chest pain, dyspnea, tachycardia, palpitations, tremor, headache, hypokalemia, hyperglycemia, nausea and vomiting, and nasal stuffiness. The RR for cessation of treatment because of adverse events was 11.3 (95 percent CI, 3.8 to 33.5). There was no difference in the rate of perinatal and neonatal deaths. Treatment had no effect on neonatal morbidity such as respiratory distress syndrome, cerebral palsy, and necrotizing enterocolitis. Two trials comparing ritodrine with terbutaline in 183 women found that patients who took terbutaline had a higher incidence of hyperglycemia. There was no difference in maternal or neonatal outcomes.

Although no improvement in infant outcomes was found in this review, most of the trials were done before antenatal corticosteroids were used routinely. Also, most of the trials were done in university hospitals. More studies must be done to determine if a 48-hour delay in delivery to allow for patient transfer and a course of corticosteroids improves outcomes. In the meantime, a short trial of tocolysis for preterm labor is reasonable if corticosteroids or transfer is indicated.