Nifedipine versus ritodrine for suppression of preterm labor; a meta-analysis.

BACKGROUND Since large randomized clinical trials comparing the effectiveness of nifedipine and ritodrine in the suppression of preterm labor are lacking, we performed a meta-analysis on the subject. METHODS We searched the databases Medline and EMBASE using the keywords 'nifedipine', 'ritodrine' and 'randomized' or 'randomised'. The studies were scored for blinding, method of randomization and type of analysis ('intention-to-treat' versus 'par protocol'). Subsequently, two by two tables were constructed using 'delay of labor by 48 hours or more', 'delay of labor beyond 36 weeks gestation', perinatal mortality, respiratory distress syndrome and admission to a neonatal intensive care unit as end points. Homogeneity between the studies was tested with a Breslow-Day test. Pooled odds ratios were calculated in case homogeneity could not be rejected. RESULTS We could detect ten studies that were published between 1986 and 1998, incorporating data of 681 patients. Nifedipine reduced the risk of delivery within 48 hours compared to ritodrine, but this difference was not statistically significant (odds ratio 0.85, 95% confidence interval 0.54 to 1.1). Nifedipine also reduced the risk of delivery before 36 weeks compared to ritodrine, and this difference was statistically significant (odds ratio 0.59, 95% confidence interval 0.39 to 0.90). We are not aware of studies reporting on long-term outcome. CONCLUSION Since studies reporting on long-term outcome are lacking, the choice between nifedipine and ritodrine can only be based on obstetrical and short-term neonatal outcomes. From that perspective, nifedipine should be the drug of first choice for the suppression of preterm labor.