A single-stage cluster sampling was followed. All the 'mouzas' (revenue villages) in Shahjadpur sub-district were divided into clusters so that each cluster contained a population of about 3,000. This generated 188 clusters. 104 out of 188 clusters-52 clusters for the intervention and 52 clusters for the control group - were randomly selected for the study to enroll the required 1300 pregnant women. Each cluster was then randomly allocated to either the intervention or control group using a computer generated random sequence. The random allocation sequence was generated independently by a statistician, who had no further involvement with the study. Once allocated, in each cluster all the eligible pregnant women were identified, invited, and enrolled during door-to-door visits by the project field staff. The field staff included female health workers, with the help of existing government community health workers such as family welfare assistants. A total of 628 eligible pregnant women were enrolled in the intervention clusters and a total of 639 eligible pregnant women in the control clusters. During the enrolment in the intervention clusters, a $100Kitchen with the improved cookstoves was installed at each of the 628 pregnant women's households following the verbal and written consent of the women and the household head.