Working more than 40 hours a week increases risk of miscarriage: Study

Pregnant women who work more than 40 hours per week or who work the night shift face an increased risk for preterm delivery and miscarriage, according to a recent University of Alberta study. Researchers reviewed 62 independent studies from 33 countries and found that longer work hours — more than 40 hours per week — was associated with a 21 per cent higher chance of preterm delivery and a 38 per cent higher chance of miscarriage.

Pregnant women working a fixed night shift had 21 per cent higher odds of preterm delivery and 23 per cent higher odds of having a miscarriage than pregnant women working a fixed day shift, the study found.

“Our body’s daily cycle is greatly influenced by ambient light in that darkness signals sleep and light signals that it’s time to wake up,” said the study’s senior researcher, Margie Davenport. “During night shift work, the day is flipped and, over time, this is thought to trigger hormonal adaptations that may influence how the baby grows and the timing of delivery.”

Working rotating shifts in comparison to a fixed day shift was associated with a 13 per cent increase in the odds of preterm delivery, a 75 per cent increase in the rate of pre-eclampsia and a 19 per cent increase in the likelihood of gestational diabetes.

While an association can be made between long working hours, fixed night shifts, rotating shifts and various health implications like preterm delivery, the researchers said they were not able to determine causation of the prenatal risks.

“There are a number of mediating factors related to work schedules that can also impact prenatal health such as smoking, leisure time, physical activity, diet and income,” said Davenport. “We didn’t observe a difference in results between studies adjusting and not adjusting for these factors. This suggests the largest influence is likely the work schedule.”

Chenxi Cai, a post-doctoral fellow who worked with Davenport on the study, said with women making up a significant proportion of the workforce, a synthesis of the data was needed to better understand the health implications of irregular work hours for pregnant women.

“Approximately 90 per cent of women remain employed during pregnancy, which is a significant number,” she said. “We wanted to evaluate the impact of shift work and long working hours during pregnancy to help women and employers make more informed decisions when it relates to occupational hours and pregnancy.”