The association between occupational factors and preterm birth: A United States nursesʹ study

OBJECTIVE: Our purpose was to evaluate factors associated with preterm birth among a national sample of U.S. nurses. STUDY DESIGN: We conducted a case-control study of 210 nurses whose infants were delivered prematurely (<37 weeks) (cases) and 1260 nurses whose infants were delivered at term (≥37 weeks) (controls). An occupational fatigue score was constructed from four sources and varied from 0 to 4. The relation between occupational activity (including hours working and fatigue score) and preterm birth was analyzed with the use of Pearson χ2 tests, estimates of odds ratios with 95% confidence intervals, and multivariate logistic regression; we controlled for confounding factors. RESULTS: Factors significantly associated with preterm birth included hours worked per week (p< 0.002), per shift (p< 0.001), and while standing (p< 0.001); noise (p = 0.005); physical exertion (p = 0.01); and occupational fatigue score (p< 0.002). The adjusted odds ratios were 1.6 (p = 0.006) for hours worked per week (≤36 vs>36) and 1.4 (p = 0.02) for fatigue score <3 vs ≥3. CONCLUSIONS: Preterm birth among working women may be related to hours worked per day or week and to adverse working conditions.