A substantial proportion of women who have an episode of threatened preterm labour (before 37 weeks) are actively treated with agents that stop the uterine contractions (tocolytic therapy) and they do not progress to give birth. After being successfully treated for an episode of threatened preterm birth, women may then take medication (tocolytics) to prolong gestation so that their baby is not born too early. Medications used for this purpose include betamimetics, magnesium sulphate, calcium channel blockers and COX inhibitors.
Oral betamimetics for maintenance therapy after threatened preterm labour do not prevent preterm labour. This conclusion is based on 13 randomised controlled trials with a total of 1551 women. In this review, the betamimetics ritodrine and terbutaline did not reduce the rate of preterm birth (eight trials), or prevent problems with babies that required admission to the neonatal intensive care unit (two trials), when compared with placebo, no treatment or other tocolytic drugs. Betamimetics may cause pregnant women to have an increased heart rate (palpitations) and rate of breathing, low blood pressure, nausea and vomiting, and high blood sugar concentrations as side effects.
Available evidence does not support the use of oral betamimetics for maintenance therapy after threatened preterm labour.
Some women who have threatened to give birth prematurely, subsequently settle. They may then take oral tocolytic maintenance therapy to prevent preterm birth and to prolong gestation.
To assess the effects of oral betamimetic maintenance therapy after threatened preterm labour for preventing preterm birth.
We updated the search of the Cochrane Pregnancy and Childbirth Group's Trials Register on 9 November 2012.
Randomised controlled trials comparing oral betamimetic with alternative tocolytic therapy, placebo or no therapy, for maintenance following treatment of threatened preterm labour.
Two review authors independently applied the selection criteria and carried out data extraction and quality assessment of studies.
We did not identify any new trials from the updated search so the results remain unchanged as follows.
We included 13 randomised controlled trials (RCTs) with a total of 1551 women. We found no differences for admission to the neonatal intensive care unit when betamimetics were compared with placebo (risk ratio (RR) 1.28, 95% confidence interval (CI) 0.68 to 2.41; two RCTs of terbutaline with 2600 women) or with magnesium (RR 0.80, 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 six RCTs, four comparing ritodrine with placebo/no treatment and two comparing terbutaline with placebo/no treatment (RR 1.11, 95% CI 0.91 to 1.35; 644 women). We observed no differences between betamimetics and placebo, no treatment or other tocolytics for perinatal mortality and morbidity outcomes. Some adverse effects such as tachycardia were more frequent in the betamimetics groups than the groups allocated to placebo, no treatment or another type of tocolytic.