A Cochrane review included 20 studies with a total of 1 509 subjects. The non-selective COX inhibitor, indomethacin was used in 15 trials. When compared with placebo, indomethacin resulted in a reduction in birth before 37 weeks' gestation in one small trial. No differences were shown when comparing COX inhibitors with magnesium sulphate (MgSO4) (RR 0.87, 95% CI 0.59 to 1.29; 7studies, n=792) or calcium channel blockers (CCBs) (RR 1.08, 95% CI 0.58 to 2.01; 2 studies, n=230) in terms of prolonging pregnancy or for any fetal/neonatal outcomes. There were also no differences in very preterm birth (before completion of 34 weeks of gestation) and no maternal deaths occurred in the one study that reported on this outcome. However COX inhibitors resulted in fewer maternal adverse affects when compared with magnesium sulphate (RR 0.39, 95% CI 0.25 to 0.62; NNT 11, 95% CI 9 to 17; 5 studies, n=635). Compared with betamimetics, COX inhibitors resulted in a reduction in birth less than 48 hours after trial entry (RR 0.27, 95% CI 0.08 to 0.96; 2 studies, n=100) and preterm birth (before completion of 37 weeks; RR 0.53, 95% CI 0.28 to 0.99; 2 studies, n=80) although no benefit was shown in terms of neonatal morbidity or mortality. COX inhibition was also associated with fewer maternal adverse affects compared with betamimetics (RR 0.19, 95% CI 0.11 to 0.31; number needed to treat (NNT) 3, 95% CI 2 to 3; 5 studies, n=248) and maternal adverse effects requiring cessation of treatment (average RR 0.09, 95% CI 0.02 to 0.49; NNT 5, CI 95% 5 to 9; 3 studies, n=166).