Shift and Night Work During Pregnancy and Preterm Birth—Cohort Study
Summary
This large Swedish cohort study followed nearly 5,000 pregnant healthcare workers to see how night-shift schedules affected preterm birth risk. Researchers found that in the first trimester, women who frequently worked three or more consecutive night shifts or had quick returns after night work (less than 28 hours off) faced a significantly higher risk of preterm birth. Frequent long shifts (10+ hours) early in pregnancy also raised risk. In the third trimester, working more than 40 hours in a week was linked to a doubled risk. The use of detailed scheduling records allowed researchers to identify that it was not just night work itself, but specific patterns — like consecutive nights and short recovery time — that mattered most.
Why It Matters For Night Shift Workers and Night Owls
For pregnant workers, this study shows that when and how shifts are scheduled can affect pregnancy outcomes. Early pregnancy appears especially sensitive: strings of consecutive night shifts, short breaks between duties, and very long shifts all increased the chance of preterm birth. Later in pregnancy, heavy weekly workloads also carried risk. For employers, the findings highlight the importance of offering safer schedules during pregnancy — such as limiting consecutive nights and providing longer rest periods. For workers, it underscores the value of discussing shift patterns with managers and healthcare providers as part of protecting both their own health and their baby’s.
Notes
Large cohort with detailed roster data.