Pregnant women who work night shifts have higher risk of preterm delivery, miscarriage: study

Working more than 40 hours a week also linked with higher odds of pregnancy complications.

Pregnant women who work night shifts and longer working hours are at increased risk for preterm delivery and miscarriage, according to a recent University of Alberta study.

An analysis of 62 independent studies from 33 countries revealed that 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.

"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, U of A pregnancy 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."

The study also indicated 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.

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."

The team also found that 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. Pre-eclampsia and gestational diabetes can have long-term health implications for both mother and baby, including Type 2 diabetes and cardiovascular disease.

Reducing the risk

Davenport and Cai encouraged pregnant women to avoid shift work and working more than 40 hours a week, if circumstances allow. However, when this isn't possible, Davenport emphasized focusing on other aspects of life within a pregnant woman's control.

"Focus on maintaining a healthy, active lifestyle outside of work. Include exercise by following the 2019 Canadian Guideline for Physical Activity Throughout Pregnancy, sufficient sleep and nutritious food to improve prenatal health."

Causes difficult to pinpoint

Although the studies reviewed in the analysis included data from 196,989 women, the information was observational. And while an association can be made between long working hours, fixed night shifts, rotating shifts and various health implications like preterm delivery, Davenport and Cai 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."

The analysis, which was published in the American Journal of Obstetrics and Gynecology and funded by the Government of Alberta Occupational Health and Safety Futures Grant, will be followed up with another study looking at how the type of work pregnant women engage in affects maternal and fetal health.