Objective This study is an economic evaluation of immediate birth compared with expectant management in women with preterm prelabour rupture of the membranes near term (PPROMT).Design A cost-effectiveness analysis alongside the PPROMT randomised controlled trial.Setting Obstetric departments in 65 hospitals across 11 countries.Population Women with a singleton pregnancy with ruptured membranes between 34 +0 and 36 +6 weeks gestation.Methods Women were randomly allocated to immediate birth or expectant management. Costs to the health system were identified and valued. National hospital costing data from both the UK and Australia were used. Average cost per recruit in each arm was calculated and 95% confidence intervals were estimated using bootstrap re-sampling. Averages costs during antenatal care, delivery and postnatal care, and by country were estimated.Main outcomes measures Total mean cost difference between immediate birth and expectant management arms of the trial.Results From 11 countries 923 women were randomised to immediate birth and 912 were randomised to expectant management. Total mean costs per recruit were £8852 for immediate birth and £8740 for expectant delivery resulting in a mean difference in costs of £112 (95% CI: À431 to 662). The expectant management arm had significantly higher antenatal costs, whereas the immediate birth arm had significantly higher delivery and neonatal costs. There was large variation between total mean costs by country.Conclusion This economic evaluation found no evidence that expectant management was more or less costly than immediate birth. Outpatient management may offer opportunities for cost savings for those women with delayed delivery.Keywords Cost-benefit analysis, delivery, fetal membranes, intensive care, neonatal/economics, neonatal sepsis, obstetric, premature birth/*prevention and control, premature rupture.Tweetable abstract For women with preterm prelabour rupture of the membranes, the relative benefits and harms of immediate and expectant management should inform counselling as costs are similar.