A complete and comprehensive search of the relevant evidence is an essential step in the preparation of a scientific systematic review. The Cochrane Pregnancy and Childbirth Database consists of some 600 systematic reviews, based on almost 6,000 randomized or quasi-randomized trials of care during pregnancy and childbirth. As ascertainment from electronic search of the National Library of Medicine MEDLINE database was not complete, the mainstay of our search strategy was a systematic hand search of some 60 journals, beginning with volumes published in 1950. Additional references were obtained from the list of references in primary research reports and conference reports. A major effort was made to identify unpublished trials and to obtain unpublished data from published trials.