New research published in Occupational & Environmental Medicine indicates a potential link between prolonged forward bending at work during pregnancy and an elevated risk of miscarriage. The extensive study, drawing on data from more than 800,000 pregnancies in Denmark, suggests a 'dose-response' pattern where increased bending time correlated with higher risk, more consistently than for standing or walking.
Professor Asma Khalil, Professor of Obstetrics and Maternal Medicine and Consultant Obstetrician at City St George’s, University of London, highlighted the study's strengths, including its large scale and the use of a pregnancy-specific job exposure matrix to estimate occupational activities. This method, she noted, helps reduce 'recall bias' compared to self-reported data. However, Professor Khalil also cautioned that as an observational study, it cannot definitively prove cause and effect. Limitations include a lack of individual smoking data for many miscarriages, inability to adjust for lifting, and potential confounding factors like shift work or chemical exposures.
Professor Khalil stressed that the findings should not be misinterpreted as meaning ordinary movement in early pregnancy is unsafe. The study specifically examined occupational patterns of exposure, particularly prolonged or repeated forward bending, rather than routine daily activities. She advised that while the research presents an intriguing hypothesis regarding workplace postures and miscarriage risk, its findings require replication and confirmation in other populations before they can be translated into precise workplace guidance.
Professor Andrew Shennan OBE, Professor of Obstetrics at King’s College London, echoed the need for caution, despite the large dataset and well-performed analysis. He pointed out that the reported effect size is very small. Like all retrospective studies, establishing causation is challenging, as there could be other reasons for the observed links. For instance, individuals in more physically demanding jobs might be more inclined to report a miscarriage as a reason for absence from work. Professor Shennan also noted that prospective studies have not found similar associations, and it is difficult to link these activities to a likely mechanism, given that many miscarriages are due to genetic reasons.
Professor Kevin McConway, Emeritus Professor of Applied Statistics at the Open University, clarified an important detail regarding the study's interpretation. He explained that when the research states, for example, 'each additional hour of bending forwards... was associated with a 36% higher risk [of miscarriage]', it refers to an additional hour of bending forward, on average, throughout the first few months of pregnancy during each 8-hour working day, rather than a single isolated hour. This clarification makes the association more plausible, as an average increase of one hour in every eight hours of work represents a substantial increase in time spent bending.