Factors associated with employment status before and during pregnancy: Implications for studies of pregnancy outcomes

Background: Potential confounding or effect modification by employment status is frequently overlooked in pregnancy outcome studies. Methods: To characterize how employed and non-employed women differ, we compared demographics, behaviors, and reproductive histories by maternal employment status for 8,343 mothers of control (non-malformed) infants in the National Birth Defects Prevention Study (1997–2007) and developed a multivariable model for employment status anytime during pregnancy and the 3 months before conception. Results: Sixteen factors were independently associated with employment before or during pregnancy, including: maternal age, pre-pregnancy body mass index, pregnancy intention, periconceptional/first trimester smoking and alcohol consumption, and household income. Conclusions: Employment status was significantly associated with many common risk factors for adverse pregnancy outcomes. Pregnancy outcome studies should consider adjustment or stratification by employment status. In studies of occupational exposures, these differences may cause uncontrollable confounding if non-employed women are treated as unexposed instead of excluded from analysis. Am. J. Ind. Med. 60:329–341, 2017. © 2017 Wiley Periodicals, Inc

Examining temporal effects on cancer risk in the international nuclear workers’ study

International audienceThe paper continues the series of publications from the International Nuclear Workers Study cohort that comprises 308,297 workers from France, the United Kingdom and the United States, providing 8.2 million person-years of observation from a combined follow-up period (at earliest 1944 to at latest 2005). These workers’ external radiation exposures were primarily to photons, resulting in an estimated average career absorbed dose to the colon of 17.4 milligray. The association between cumulative ionizing radiation dose and cancer mortality was evaluated in general relative risk models that describe modification of the excess relative risk (ERR) per gray (Gy) by time since exposure and age at exposure. Methods analogous to a nested-case control study using conditional logistic regression of sampled risks sets were used. Outcomes included all solid cancers, lung cancer, leukemias excluding chronic lymphocytic, acute myeloid leukemia, chronic myeloid leukemia, multiple myeloma, Hodgkin lymphoma and non-Hodgkin lymphoma. Significant risk heterogeneity was evident in chronic myeloid leukemia with time since exposure, where we observed increased ERR per Gy estimates shortly after exposure (2–10 year) and again later (20–30 years). We observed delayed effects for acute myeloid leukemia although estimates were not statistically significant. Solid cancer excess risk was restricted to exposure at age 35+ years and also diminished for exposure 30 years prior to attained age. Persistent or late effects suggest additional follow-up may inform on lifetime risks. However, cautious interpretation of results is needed due to analytical limitations and a lack of confirmatory results from other studies. © 2016 UIC