A Cochrane review included 20 studies, of which 12 trials, involving a total fo 1 367 women, compared betamimetics with placebo. As compared with placebo, betamimetics decreased the number of women in preterm labour giving birth within 48 hours (relative risk (RR) 0.68; 95% CI 0.53–0.88; 10 trials, n=1209). There was a trend towards a decrease in the number of births within seven days (RR 0.80; 95% CI 0.65 to 0.98;5 trials, n=911). No benefit was demonstrated for betamimetics on perinatal death (RR 0.84; 95% CI 0.46–1.55, 11 trials, n = 1332), or neonatal death (RR 1.90; 95% CI 0.27–3.00, 6 trials, n = 1174). No significant effect was demonstrated for respiratory distress syndrome (RR 0.87; 95% CI 0.71–1.08, 8 trials, n = 1239). Betamimetics were significantly associated with the following: withdrawal from treatment due to adverse effects; chest pain; dyspnoea; tachycardia; palpitation; tremor; headaches; hypokalemia; hyperglycemia; nausea/vomiting; and nasal stuffiness; and fetal tachycardia. Nine trials compared different types of betamimetics. Other betamimetics were compared with ritodrine in five trials (n = 948). Other comparisons were examined in single trials: hexoprenaline compared with salbutamol (n = 140), slow versus moderate release salbutamol (n = 52) and salbutamol compared with terbutaline (n = 200). Trials were small, varied and of insufficient quality to delineate any consistent patterns of effect.
Another Cochrane review (abstract , review ) assessing oral betamimetic maintenance therapy after threatened preterm labour included 13 studies with a total of 1 551 subjects. No differences were seen for admission to the neonatal intensive care unit when betamimetics were compared with placebo (relative risk 1.28, 95% CI 0.68 to 2.41 ; 2 RCTs of terbutaline with 2 600 women) or with magnesium (RR 1.11, 95% CI 0.43 to 1.46; one RCT of 137 women). The rate of preterm birth (less than 37 weeks) showed no significant difference in 6 RCTs, 4 comparing ritodrine with placebo/no treatment and two comparing terbutaline with placebo/no treatment (RR 1.08, 95% CI 0.91 to 1.35, 644 women). No differences between betamimetics and placebo, no treatment or other tocolytics were seen for perinatal mortality and morbidity outcomes.
A systematic review including 17 studies with a total of 1184 women was abstracted in DARE. Tocolytics were associated with significant decreases in the likelihood of delivery within 24 hours (OR 0.47, 95% CI 0.29 to 0.77), but they were not associated with a statistically significant reduction in prenatal death (OR 1.22, 95% CI 0.84 to 1.78), respiratory distress syndrome (OR 0.82, 95% CI 0.64 to 1.07), intraventricular haemorrhage (OR 0.73, 95% CI 0.46 to 1.15), neonatal sepsis, seizures, hypoglycaemia, or birth weight under 2500 g.
Another Cochrane review (abstract , review ) included one trial with 64 singleton pregnancies comparing oral betamimetic agent isoxuprine with placebo. No difference was seen for perinatal mortality rate (RR 4.74, 95% CI 0.50 to 45.00), for reduction of spontaneous onset of preterm labour (RR 1.07, 95% CI 0.14 to 8.09) or preterm birth, less than 37 weeks' gestation, or for birthweight less than 2500 grams (RR 1.74, 95% CI 0.44 to 6.87) or neonatal death (RR 4.74, 95% CI 0.50 to 45.00).
The following decision support rules contain links to this evidence summary: