Full-time exposure to occupational noise during pregnancy was associated with reduced birth weight in a nationwide cohort study of Swedish women.

Noise is a common exposure in the occupational work environment. Earlier studies of occupational noise and pregnancy outcome are few and show mixed results. To investigate if objectively assessed exposure to occupational noise during pregnancy is associated with reduced intrauterine growth and/or preterm birth a nationwide cohort study of 857,010 single births was initiated. Individual information on occupation and risk factors was retrieved from prenatal care interviews at pregnancy week 10. Occupational noise was classified into three exposure categories <75, 75-85, >85 dBA by a job exposure matrix. Odds ratios were adjusted for BMI, smoking, parity, education, physically strenuous work and low job control. Exposure to high (>85 dBA) levels of occupational noise throughout the pregnancy (full time workers) was associated with an increased risk of the child being born small for gestational age, OR 1.44 (95% CI 1.01 to 2.03) compared to noise exposure <75 dBA. A similar increase was seen for low birth weight OR 1.36 (95% CI 1.03 to 1.80) for high levels of noise. No clear association was seen for preterm birth. No consistent effects on birth outcome was observed in women who had worked part-time or were on leave of absence >21 days (median). In summary, full-time exposure to high levels of noise during pregnancy was associated with a slightly reduced fetal growth but not with preterm birth. The effect of intermediate occupational noise exposure (75-85 dBA) showed a small, but statistically increased risk for all studied birth outcomes. The study strengthens the evidence that pregnant women should not be long-term exposed to high levels >85 dBA of occupational noise during pregnancy. Intermediate exposure should be studied further.