Physical workload during pregnancy and adverse pregnancy outcomes: results from a Danish nationwide occupational register-based pregnancy cohort (DOC*X-Generation).

Objectives: The objective was to investigate if high physical workload during pregnancy is associated with adverse pregnancy outcomes.

Methods: The register-based cohort, DOC*X-Generation included employed pregnant women in Denmark (1977-2018). A summary score of physical workloads, based on a job exposure matrix with eight physical work activities, was linked to the job held during pregnancy (coded by DISCO-88). The exposure was divided into five groups from low to high exposure. Data on miscarriages were retrieved from the Danish National Patient Register. Preterm birth (PTB) and small for gestational age (SGA) were determined by gestational age and birth weight from the Danish Medical Birth Register. Other nationwide registers provided data on potential confounders.

Results: We included pregnancies for approximately 1 million unique women where 13% terminated in miscarriages (of ~1.9 million pregnancies), 5% were PTB (of ~1.5 million pregnancies) and 13% were SGA (of ~1.6 million pregnancies). Employment in occupations with high physical workload was associated with increased risk of all three outcomes in a dose-dependent manner. For the highest compared with the lowest exposed group, adjusted ORs were 1.24 (95% CI 1.22 to 1.27) for miscarriage, 1.15 (95% CI 1.12 to 1.19) for overall PTB and 1.12 (95% CI 1.10 to 1.14) for SGA.

Conclusions: This study, based on an unselected cohort of employed women over a 40-year period, corroborates previous findings of an increased risk of adverse pregnancy outcomes due to high physical workload during pregnancy. A general recommendation to decrease the overall occupational workload of pregnant women might prevent adverse pregnancy outcomes.