Night work has been associated with adverse effects in terms of reproductive health. Specifically, menstruation has been suggested to be negatively impacted by night work, which again may influence fertility. This study investigated whether working nights is related to menstrual characteristics and if there is a relationship between shift work disorder (SWD) and menstruation. The study was cross-sectional, response rate 38%. The sample comprised female nurses who were members of the Norwegian Nurses Association; below 50 yr of age, who were not pregnant, did not use hormonal pills or intrauterine devices and who had not reached menopause (n=766). The nurses answered a postal survey including questions about night work and menstrual characteristics. Fifteen per cent reported to have irregular menstruations. Thirty-nine per cent of the nurses were classified as having SWD. Logistic regression analyses concerning the relationship between irregular menstruations and night work did not show any associations. Furthermore, no associations were found between cycle length or bleeding period and night work parameters. No associations were found between menstrual characteristics and SWD.
