Wiley, Paediatric and Perinatal Epidemiology, 1(24), p. 24-30, 2010
DOI: 10.1111/j.1365-3016.2009.01074.x
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Previous research has described variability in menstrual cycle lengths within and across women, though less attention has focused on characterising patterns of bleeding. While clinical definitions for menstrual bleeding are often given in standard textbooks, the validity of conventional definitions has not been empirically evaluated in epidemiological studies. The definition of menstrual bleeding may affect the analysis of time to pregnancy and pregnancy dating that relies upon the last menstrual period. We used daily records of vaginal bleeding from a prospective cohort study that included 74 women trying to become pregnant who reported 430 bleeding episodes. A longitudinal mixture model (PROC TRAJ) was used to classify patterns of bleeding.