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Working conditions and adverse pregnancy outcome: a meta-analysis

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Abstract

Objective: To evaluate the association between working conditions and adverse pregnancy outcomes by performing a meta-analysis of published studies.

Data Sources: We searched the English-language literature in MEDLINE through August 1999 using the terms standing, posture, work, workload, working conditions, shift, occupational exposure, occupational diseases, lifting, pregnancy complications, pregnancy, small for gestational age (SGA), fetal growth retardation (FGR), preterm, and labor.

Methods of Study Selection: We included observational studies evaluating the effect of one or more of the following work-related exposures on adverse pregnancy outcome: physically demanding work, prolonged standing, long work hours, shift work, and cumulative work fatigue score. Outcomes of interest were preterm birth, hypertension or preeclampsia, and SGA.

We conducted a meta-analysis based on 160,988 women in 29 studies to evaluate the association of physically demanding work, prolonged standing, long working hours, shift work, and cumulative work fatigue score with preterm birth. Also analyzed were the associations of physically demanding work with hypertension or preeclampsia and SGA infants. The data were analyzed using the Peto-modified Mantel-Haenszel method to estimate the pooled odds ratios (ORs) and 95% confidence intervals (CIs).

Tabulation, Integration, and Results: Physically demanding work was significantly associated with preterm birth (OR 1.22, 95% CI 1.16, 1.29), SGA (OR 1.37, 95% CI 1.30, 1.44), and hypertension or preeclampsia (OR 1.60, 95% CI 1.30, 1.96). Other occupational exposures significantly associated with preterm birth included prolonged standing (OR 1.26, 95% CI 1.13, 1.40), shift and night work (OR 1.24, 95% CI 1.06, 1.46), and high cumulative work fatigue score (OR 1.63, 95% CI 1.33, 1.98). We found no significant association between long work hours and preterm birth (OR 1.03, 95% CI 0.92, 1.16).

Conclusion: Physically demanding work may significantly increase a woman’s risk of adverse pregnancy outcome.

Section snippets

Data sources

Relevant studies were identified by a computer search of English-language abstracts in the MEDLINE database for the years 1966 to August 1999. A variety of searches were conducted using combinations of the following medical subject heading terms: standing, posture, work, workload, working conditions, shift, occupational exposure, occupational diseases, lifting, pregnancy complications, pregnancy, small for gestational age (SGA), fetal growth restriction (FGR), preterm, and labor. We

Methods of study selection

We followed the systematic guidelines proposed by Thacker et al38 for meta-analysis. We extracted 58 articles using this search strategy, of which 29 met the eligibility criteria. Through personal communications with authors who provided restratified data, we were able to include six studies39, 40, 41, 42, 43, 44 that did not initially meet our eligibility criteria for some or all comparisons. Prospective cohort, cross-sectional, and case control studies examining the association between

Tabulation, integration, and results

Our outcomes of interest were preterm birth, hypertension or preeclampsia, and SGA. We constructed two-by-two tables from data provided in the original papers. Because some, but not all, original authors adjusted their odds ratios (ORs) on the basis of demographic data, we used raw data from the studies rather than ORs. The meta-analysis was conducted using the Peto-modified Mantel-Haenszel method,69 and the results confirmed using the DerSimonian and Laird random effects method.70 Ninety-five

Discussion

Our analyses suggest that working conditions may significantly influence a woman’s risk of an adverse pregnancy outcome. The significant positive associations between physically demanding work and prolonged standing with preterm birth, and between physically demanding work with SGA did not vary by meta-analytic method or by subgroup analysis. Likewise, the associations between high cumulative work fatigue score and shift work with preterm birth, and between physically demanding work and

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