Printed in U.S.A. DOI: 10.1093/aje/kwf046 Serum Dioxin Concentrations and Menstrual Cycle Characteristics

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a widespread industrial environmental contaminant. Animal studies suggest that TCDD exposure alters the estrus cycle. Twenty years after a 1976 industrial explosion in Seveso, Italy, the authors interviewed female residents to determine whether there was an association between TCDD exposure and current menstrual cycle characteristics. The authors analyzed serum samples collected soon after the explosion to quantify individual TCDD levels. Among women who were premenarcheal at the time of the explosion, a 10-fold increase in serum TCDD level was associated with a lengthening of the menstrual cycle by 0.93 days (95 % confidence interval (CI): –0.01, 1.86) and a reduction in the odds of scanty menstrual flow (adjusted odds ratio = 0.33, 95 % CI: 0.10, 1.06). However, among women who were postmenarcheal at the time of the explosion, TCDD was not associated with menstrual cycle length (adjusted β = –0.03 days, 95 % CI: –0.61, 0.54) or scantiness of flow (adjusted odds ratio = 1.36, 95 % CI: 0.70, 2.64). In both menarche groups, TCDD levels were associated with decreased odds of having irregular cycles (adjusted odds ratio = 0.46, 95