Prophylactic oral betamimetics for reducing preterm birth in women with a twin pregnancy.

BACKGROUND: Twin pregnancies are associated with a high risk of neonatal mortality and morbidity due to an increased rate of preterm birth. Betamimetics can decrease contraction frequency or delay preterm birth in singleton pregnancies by 24 to 48 hours. The efficacy of oral betamimetics in women with a twin pregnancy is unproven. OBJECTIVES: To assess the effects of prophylactic oral betamimetics administered to women with twin pregnancies. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group Trials Register (May 2004), CENTRAL (The Cochrane Library, Issue 2, 2004), MEDLINE (January 1966 to May 2004), EMBASE (January 1985 to May 2004), and reference lists. SELECTION CRITERIA: Randomized controlled trials in twin pregnancies comparing oral betamimetics with placebo or any intervention with the specific aim of preventing preterm birth. DATA COLLECTION AND ANALYSIS: Standard methods of The Cochrane Collaboration and the Cochrane Pregnancy and Childbirth Group were used. Trials were independently assessed for methodological quality by at least two authors, who extracted data using a data collection form. MAIN RESULTS: Five trials (344 twin pregnancies) were included. All trials compared oral betamimetics to placebo. Betamimetics reduced the incidence of preterm labour (one trial, 50 twin pregnancies, relative risk (RR) 0.40; 95% confidence interval (CI) 0.19 to 0.86). However, betamimetics did not reduce preterm birth less than 37 weeks' gestation (four trials, 276 twin pregnancies, RR 0.85; 95% CI 0.65 to 1.10) or less than 34 weeks' gestation (one trial, 144 twin pregnancies, RR 0.47; 95% CI 0.15 to 1.50). Mean neonatal birthweight in the betamimetic group was significantly higher than in the placebo group (three trials, 478 neonates, weighted mean difference 111.2 grams; 95% CI 22.2 to 200.2). Nevertheless, there was no evidence of an effect of betamimetics in reduction of low birthweight (two trials, 366 neonates, RR 1.19; 95% CI 0.77 to 1.85) or small-for-gestational age neonates (two trials, 178 neonates, RR 0.92; 95% CI 0.52 to 1.65). Two trials (388 neonates) showed that betamimetics significantly reduced the incidence of respiratory distress syndrome but the difference was not significant when the analysis was adjusted for correlation of babies from twins. Three trials (452 neonates) showed no evidence of an effect of betamimetics in reducing neonatal mortality (RR 0.80; 95% CI 0.35 to 1.82). AUTHORS' CONCLUSIONS: There is insufficient evidence to support or refute the use of prophylactic oral betamimetics for preventing preterm birth in women with a twin pregnancy.