Authors
Cooper GS, Klebanoff MA, Promislow J, Brock JW, Longnecker MP.

Title
Polychlorinated biphenyls and menstrual cycle characteristics

Source
Epidemiology 2005 Mar; 16(2):191-200

Summary
Persistent organochlorine pollutants such as polychlorinated biphenyls (PCBs), and pollutants like, p,p-DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene), the major metabolite of dichlorodiphenyltrichloroethane (DDT), have been shown to have effects on the endocrine system at background exposure levels. Animal experiments have suggested a possible role of these pollutants on menstrual cycle characteristics; however there are few human studies and these findings are contradictory.

The current study explored the effects of exposure to PCBs and DDE on the menstrual cycle characteristics of women enrolled in the collaborative perinatal project, a prospective cohort study of pregnant women enrolled from 12 centers in the US between 1959 and 1965. The study was designed to examine the etiology of neurological disorders and other conditions in children. Details about pre-pregnancy menstrual cycle including cycle length, regularity, and bleeding duration, were obtained at the onset of the study. Serum levels of eleven PCB congeners, DDE, p,p-DDT, cholesterol, and triglycerides were measured from stored blood samples that were obtained at the time of enrollment. In addition, information on potential confounding variables such as: age, race, pre-pregnancy body mass index, socioeconomic index, smoking history, age at menarche, parity, and pregnancy interval were also collected.

A total of 2,314 subjects were included in the analysis with women using oral contraceptives and women with missing information about exposures, menstrual cycle characteristics, or confounders excluded. Exposure to DDE or PCBs was categorized into five groups based on the wet-weight or serum lipid measurements from blood samples. Two subgroup analyses were performed to assess misclassification; first by limiting analysis to primiparous women, and second by excluding women who delivered a live baby in the two years prior to enrollment.

No associations were observed between mean bleeding duration, prevalence of heavy bleeding, and dysmenorrhea and levels of DDE or PCBs. No association was observed between DDE and cycle length. However, subgroup analyses indicated a possible effect of DDE and PCBs on irregularity of the menstrual cycle. Increasing serum levels of PCBs were significantly associated with longer cycles (0.7 day difference in the highest versus the lowest exposure category overall).

In summary, this study noted that exposure to PCBs increased menstrual cycle length. In addition, although, the evidence was weak, this study also suggested a potential effect of DDE and PCBs on irregular cycles. Large sample size is an advantage of this study. It should be noted that this is the first large study that examined the relationship between low-level exposure to PCBs and DDE and menstrual cycle characteristics. This study was based on self-reported menstrual cycle characteristics, which is an important limitation, as recall may not be accurate. Other important limitations may include: lack of a precise definition for irregular cycles, and the lack of specific definitions for amount of flow, and the categorization of dysmenorrhea based on self reported impact of pain, such as, need for medication or difficulty in performing regular daily activities (as compared to actual pain intensity). Overall this study indicated an effect of low dose PCB exposure on certain menstrual cycle characteristics.