Three RCTs were included in the analysis (data from 648 women and 643 infants followed up). The women received progestational agents (n=399) or placebo (n=249).
All of the trials were double-blind. Two trials described the method of randomisation and the third reported concealment of allocation.
The use of progestational agents resulted in a statistically significantly lower risk of delivery less than 37 weeks' gestation than the placebo group (RR 0.57, 95% CI: 0.36, 0.90; 3 RCTs). There were no statistically significant effects on the risks of congenital anomalies (2 RCTs), spontaneous abortion (3 RCTs) or perinatal death (2 RCTs). There was no reported statistical heterogeneity in any of the pooled analyses.
Individual trials comparing progestational treatment with placebo showed statistically significant results for lower risk of delivery before 35 weeks' (RR 0.67, 95% CI: 0.48, 0.93), 34 weeks' (RR 0.15, 95 % CI: 0.04, 0.64) and 32 weeks' (RR 0.58, 95% CI: 0.37, 0.91) gestation. In addition, the risk of birth weight less than 2,500g was lower (RR 0.66, 95% CI: 0.51, 0.87) and mean birth weight was higher (WMD 475.0, 95% CI: 16.56, 933.44) in the treatment groups.