Results from a systematic review and meta-analysis suggest that fears about substantially increased miscarriage risks in women working shifts, long hours, and in jobs involving moderate-to-high physical workload may be largely unfounded.
As reported in the Scandinavian Journal of Work and Environmental Health, Jens Peter Bonde, from Copenhagen University in Denmark, and colleagues reviewed 30 articles assessing the relative risk for miscarriage associated with various types of occupational activities.
Overall, 13 studies assessed the effects of shift work, 10 the influence of long working hours, 18 the effects of lifting, eight the impact of long periods of standing, and five the effects of physical workload. The women worked in a range of occupational areas including healthcare, agriculture, textile industry, dry cleaning, and the pharmaceutical industry.
The team found that, of the activities evaluated, working on a fixed night shift was associated with the highest risk for miscarriage, at a 51% relative risk increase compared with working during the day, although the risk for these women was still only moderate.
Working for 40-52 hours per week, lifting more than 100 kg/day, standing for more than 6-8 hours/day, and having a moderate-to-high physical workload also increased the relative risk for miscarriage, but only by 12-36%.
The researchers note that when less high-quality articles were excluded from the analysis, the risk increases associated with long periods of standing and long working hours were smaller.
"These largely reassuring findings do not provide a strong case for mandatory restrictions in relation to shift work, long working hours, occupational lifting, standing, and physical workload" for pregnant women, say Bonde et al.
However, while they maintain that evidence does not currently support compulsory restrictions for pregnant women, they say that "there is a pressing need to conduct more and better prospective investigations, with enrolment of women before or during the very early stages of pregnancy."
They also suggest that "notwithstanding the generally reassuring nature of this review, it may be prudent to advise women against work entailing high levels of such exposures during the first trimester of pregnancy."
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