Background: Occupational activities are suspected of having an adverse impact on pregnancy outcome. We assessed the evidence relating three major adverse outcomes (pre-term delivery, low birthweight and pre-eclampsia/gestational hypertension) to five common occupational exposures (prolonged working hours, shift work, lifting, standing, and heavy physical workload). Methods: We conducted a systematic search of MEDLINE and EMBASE (1966-Dec 2005) using combinations of keywords and MeSH terms. For each relevant paper we abstracted standard details that were then used to summarise the design features of studies, to rate their methodological quality (completeness of reporting, and potential for important bias or confounding), and to provide estimates of effect. For studies with similar definitions of exposure and outcome we calculated pooled estimates of relative risk in meta-analysis. Results: Our search identified 53 reports – 35 concerning pre-term delivery, 34 on birthweight and nine about pre-eclampsia or gestational hypertension. These included 21 cohort investigations. For pre-term delivery we found extensive evidence relating to each of the exposures of interest. Findings were generally consistent and tend to rule out a more than moderate effect size (RR greater than 1.4). The larger and most complete studies were less positive, and pooled estimates of risk pointed to only modest or null effects. For small for gestational age (SGA), the position was similar, but the evidence base was more limited. For pre-eclampsia and gestational hypertension it was too small to allow firm conclusions. Conclusions: The balance of evidence is not sufficiently compelling to justify mandatory restrictions on any of the activities considered in this review. However, given some uncertainties in the evidence base and the apparent absence of important beneficial effects, it may be prudent to advise against long working hours, prolonged standing, and heavy physical work, particularly late in pregnancy. Our review identifies several priorities for future investigation.
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