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This paper reports results of a nested case-control sub-study of women who were participants in a randomized controlled trial of oral versus vaginal metronidazole treatment for bacterial vaginosis in the first trimester of pregnancy. This flow diagram shows how sub-study cases (women with preterm delivery) and controls (women with term delivery) were chosen from parent study groups randomized to oral or vaginal metronidazole treatment, with reasons for subject exclusion.
