A Cochrane review included 6 studies with 794 subjects. No difference in the incidence of preterm birth (RR 0.97; 95% CI 0.87 to 1.09; 5 trials, n=681), birth within 48 hours of treatment (RR 0.46; 95% CI 0.07 to 3.00; 2 trials, n=128) or neonatal mortality (average RR 0.75; 95% CI 0.05 to 11.76; 2 trials, 133 infants) were found when calcium channel blocker (nifedipine) maintenance therapy was compared with placebo or no treatment. Women receiving nifedipine maintenance therapy were significantly more likely to have their pregnancy prolonged (mean difference (MD) 5.35 days; 95% CI 0.49 to 10.21; four trials, 275 women); however, no differences between groups were shown for birth at less than 34 weeks' gestation, birth at less than 28 weeks' gestation, birth within seven days of treatment, or gestational age at birth.
Comment: The quality of evidence is downgraded by study quality (unclear blinding, possible selective outcome reporting bias).