Night shift work undertaken by women and fertility treatment interact to increase prevalence of urogenital anomalies in children

Abstract

Objective To investigate the role of maternal night shift work in occurrence of urogenital anomalies in offspring, considering a possible interaction with mode of conception. Methods A population-based cohort comprising births in South Australia (1986–2002) was produced via linkage of fertility clinic records, perinatal and birth defects data. This study concerned first births to women in paid employment (n=98\u2009103). Potential exposure to night shift was imputed by applying a job-exposure matrix to recorded occupation. Associations were examined using logistic regression, first for nurses and other night shift workers separately, then combined. An interaction term for night shift work and mode of conception was included in all models, while adjusting for covariates. Results Associations were similar for nurses and other night shift workers, although only statistically significant for the former when considered separately. A multiplicative interaction was supported: for natural conceptions, maternal night shift work was not associated with offspring urogenital anomalies (OR=0.99, 95%\u2009CI 0.84 to 1.15); where a birth arose from fertility treatment, urogenital anomalies were significantly higher among births to all night shift workers compared with day workers (OR=2.07, 95%\u2009CI 1.20 to 3.55). This was not due to differences in the type of fertility treatment received. Conclusions Women in occupations that probably involved night shift did not have offspring with increased prevalence of urogenital anomalies if they conceived naturally. When night shift workers conceived with fertility treatment, the prevalence of urogenital anomalies was elevated. Possibly these women had the greatest exposure to night shift work, or least tolerance for this work schedule, or heightened sensitivity to hormonal aspects of fertility treatment.