Assuming the Level of significance = 5%, Power = 80%, Type of test = two-sided Based on the above stated assumptions, the initial sample size required per group is 94. To estimate the sample size for a cluster randomized trial, we needed an estimate of the degree of clustering at the practice level, which was available from a previous randomized trial of postnatal care . Using the approach of a previous study, and taking the inter-practice correlation coefficient to be 0.005 as indicated in that trial, we inflated the sample size by 2.45 times from a non-cluster randomized trial considering the potential cluster design effect. This yielded an estimated sample size in each group to be 230. Hence total sample size required for the two arm trial is 460.