title: Prophylactic oral betamimetics for reducing preterm birth in women with a twin pregnancy.
abstract: 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.
  
  
  OBJECTIVE
  To assess the effectiveness of prophylactic oral betamimetics for the prevention of preterm labour and birth for women with twin pregnancies.
  
  
  METHODS
  We searched the Cochrane Pregnancy and Childbirth Group Trials Register (31 January 2012), the Central Register of Controlled Trials (The Cochrane Library 2012, Issue 2), MEDLINE (January 1966 to 1 February 2012) and EMBASE (January 1985 to 1 February 2012).
  
  
  METHODS
  Randomised controlled trials in twin pregnancies comparing oral betamimetics with placebo or any intervention with the specific aim of preventing preterm birth. Quasi-randomised controlled trials, cluster-randomised trials and cross-over trials were not included.
  
  
  METHODS
  Two review authors independently assessed trials for inclusion and trial quality. Two review authors extracted data. Data were checked for accuracy.
  
  
  RESULTS
  Six trials (374 twin pregnancies) were included, but only five trials (344 twin pregnancies) contributed data. All trials compared oral betamimetics with placebo.Betamimetics reduced the incidence of preterm labour (one trial, 50 twin pregnancies, risk ratio (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, mean difference 111.22 g; 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, average RR 1.19; 95% CI 0.77 to 1.85, random-effects) 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).
  
  
  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.
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine Vajira Hospital, Navamindradhiraj University, Bangkok, Thailand. iammammy@hotmail.com.
authors.forename: Waralak
authors.initials: W
authors.lastname: Yamasmit
authors.forename: Surasith
authors.initials: S
authors.lastname: Chaithongwongwatthana
authors.forename: Jorge E
authors.initials: JE
authors.lastname: Tolosa
authors.forename: Sompop
authors.initials: S
authors.lastname: Limpongsanurak
authors.forename: Leonardo
authors.initials: L
authors.lastname: Pereira
authors.forename: Pisake
authors.initials: P
authors.lastname: Lumbiganon
mesh_terms: D000284:Administration, Oral; D000318:Adrenergic beta-Agonists / Q000008:administration & dosage*; D000328:Adult; D000420:Albuterol / Q000008:administration & dosage; D005260:Female; D005280:Fenoterol / Q000008:administration & dosage; D005865:Gestational Age; D006801:Humans; D007556:Isoxsuprine / Q000008:administration & dosage; D011247:Pregnancy; D059285:Pregnancy, Twin; D047928:Premature Birth / Q000517:prevention & control*; D016032:Randomized Controlled Trials as Topic; D012312:Ritodrine / Q000008:administration & dosage; D013726:Terbutaline / Q000008:administration & dosage; D015149:Tocolytic Agents / Q000008:administration & dosage*
chemical_list: D000318:Adrenergic beta-Agonists; D015149:Tocolytic Agents; D005280:Fenoterol; D012312:Ritodrine; D013726:Terbutaline; D000420:Albuterol; D007556:Isoxsuprine