Pre-pregnancy shift work's influence on postpartum weight retention: Body mass index's role.

Shift work is a prevalent workplace exposure, which increases the possibility of unhealthy behaviours and circadian rhythm disruptions and elevates the risk of metabolic diseases and adverse reproductive outcomes. But its potential of increasing the risk of postpartum weight retention remains uncertain. This study aimed to investigate the association between maternal shift work prior to conception and postpartum weight retention, and to identify modifiable factors during pregnancy for prevention. We analysed data from the Taiwan Birth Cohort Study, a prospective cohort of Taiwanese women who gave birth in 2005. We examined the pre-conceptional shift work status of 13,575 mothers and their body weight before pregnancy, before delivery, six and eighteen months after delivery. We used multivariable linear models to examine associations and effect modifications. Maternal shift work before pregnancy was significantly associated with increased postpartum weight retention at six and eighteen months (β-estimate for six months: 0.19-kilogram, 95% CI: 0.03-0.34; eighteen months: 0.23-kilogram, 95% CI: 0.04-0.40). The association between shift work and weight retention at six months postpartum was stronger among mothers who were overweight or obese before pregnancy than mothers with normal weight. This study showed the impact of shift work on postpartum weight retention and suggested a stronger association among mothers with overweight or obesity before pregnancy.