The Association Between Occupational Factors and Preterm Birth: A United States Nurses' 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 < .002), per shift (P < .001), and while standing (P < .001); noise (P = .005); physical exerton (P = .01); and occupational fatigue score (P < .002). The adjusted odds ratios were 1.6 (P = .006) for hours worked per week (≤36 vs ≶ 36) and 1.4 (P = .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.