Strenuous working conditions and birthweight, Norway 1989

To examine whether strenuous working conditions in pregnancy are associated with reduced birthweight.

Cross-sectional, population based study. Retrospective data collection by questionnaire to parturients in all maternity wards in Norway 16.10-26.11.89, completed before discharge from hospital, with response rate 87.2%. The study population consists of the 5388 women with singleton births, of whom 3321 were in paid work beyond the third month of pregnancy. Main outcome measures are prevalence of birthweight <2500 grams (LBW) and mean birthweight.

Strenuous working conditions increased risk of LBW, but only for nullipara, particularly non-smoking nullipara. Odds ratios with 95% confidence intervals for non-smoking nullipara, adjusted for age, education and income, were 0.3 (0.1,0.9) for influence on work pace, 2.8 (1.2,6.5) for exposure to heavy lifting and 2.2 (0.8,5.8) for twisting/bending. Four groups of occupations were defined according to exposure, solely based on reports from mothers with non-LBW children in order to avoid recall bias. Prevalence of LBW increased from 0.8% in the least exposed to 8.3% in the most exposed group. (Test for trend: p<0.05, after adjustment for age, education and income.) Strenuous working conditions had no independent effect on mean birthweight after adjustment for age, education, income and smoking.

Strenuous work increased the risk of LBW in nulliparae, particularly in non-smokers. Lack of influence on work pace was the strongest risk factor. The preventive effect of job modification in pregnancy may parallel smoking cessation.