Jiang C, et al. - Authors aimed at ascertaining if the pre-pregnancy exposure of hair dye and irregular menstruation were associated with the risk of abnormal birth weight. A nested case-control study was conducted from a prospective cohort of 6,203 pregnant women. This study demonstrated that either pre-pregnancy hair dye use or irregular menstruation was associated with abnormal birth weight in China. Thereby suggesting pre-pregnancy exposure to hair dye and irregular menstruation as potential risk factors for abnormal birth weight infants.