Fourteen RCTs (n=7,545) were included in the review.
There were 3 RCTS (n=1,827) of macrolides. The pre-term birth rate was significantly lower in the group receiving erythromycin with (2 RCTs) or without (1 RCT) metronidazole (OR 0.72, 95% CI: 0.56, 0.93, p=0.01). Findings for mean gestational age at delivery (1 RCT) were not statistically significant.
There were 5 RCTs (n=1,528) of clindamycin. The pre-term birth rate was significantly lower in the group receiving clindamycin (OR 0.68, 95% CI: 0.49, 0.95, p=0.02; 5 RCTs) , as was the gestational age at delivery (38.8 versus 38.0 weeks, p=0.04; 1 RCT).
There were 8 RCTs (n=5,529) of metronidazole. No significant difference was found between the groups for any outcome when metronidazole with (2 RCTs) or without (6 RCTs) erythromycin was compared with controls. When RCTs of metronidazole alone were pooled, there was a significantly higher rate of pre-term delivery in the intervention group (OR 1.31, 95% CI: 1.08, 1.58, p=0.005; 6 RCTs).
The results of subgroup analyses were also reported.