Research
Obstetrics
Occupational factors and risk of preterm birth in nurses

Presented at the 19th Annual Meeting of the Society for Pediatric and Perinatal Epidemiologic Research, Seattle, WA, June 19-20, 2006, and the 39th Annual Meeting of the Society for Epidemiologic Research, Seattle, WA, June 21-23, 2006.
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Objective

We evaluated first-trimester exposures and the risk of preterm birth in the most recent pregnancy of participants of the Nurses' Health Study II.

Study Design

Log binomial regression was used to estimate the relative risk (RR) for preterm birth in relation to occupational risk factors, such as work schedule, physical factors, and exposures to chemicals and x-rays, adjusted for age and parity.

Results

Part-time work (≤ 20 hours a week) was associated with a lower risk of preterm birth [RR, 0.7; 95% confidence interval [CI], 0.6-0.9]. Working nights was associated only with early preterm birth (< 32 weeks of gestation) (RR, 3.0; 95% CI, 1.4-6.2). Although based on only 11 exposed preterm cases, self-reported exposure to sterilizing agents was associated with an increased risk (RR, 1.9; 95% CI, 1.1-3.4).

Conclusion

These data suggest that night work may be related to early but not late preterm birth, whereas physically demanding work did not strongly predict risk.

Section snippets

Study population

The Nurses' Health Study II is a national cohort study of 116,608 US female nurses aged 25-42 years at enrollment, established in 1989.7

Follow-up questionnaires are mailed every 2 years. On the 2001 biennial questionnaire, participants were asked whether they: (1) had a pregnancy since 1993; (2) worked as a nurse during the most recent of these pregnancies; and (3) would be willing to participate. An occupational supplement was mailed to women who answered yes to all 3 questions to assess

Results

Among 6977 pregnancies ending in singleton live births during which the mother reported working as a nurse in the first trimester, 588 (8%) delivered before the 37th week from LMP. Of those who reported preterm birth, 524 (89%) delivered between 32 and 36 weeks from LMP, 47 (8%) between 28 and 31 weeks, 15 (3%) between 24 and 27 weeks, and 2 (0.3%) between 20-23 weeks. Delivery was medically indicated in 40% of the study pregnancies. The prevalence of preterm birth was 9% for spontaneous births

Comment

In this large cohort of nurses, women who worked part time had a lower risk of delivering preterm, although there was not a clear dose-response relationship with overtime hours. Nurses who worked night shift had a 3-fold risk of delivering early preterm (< 32 weeks) but not with later preterm (32-36 weeks). The risk of preterm birth was moderately associated with reported exposure to sterilizing agents; however, because there were few exposed women, this finding should be interpreted

Acknowledgment

The authors gratefully acknowledge the contributions of Walter Willett, Lynne Pinkerton, James Boiano, and Julie Tackett.

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    Cite this article as: Lawson CC, Whelan EA, Hibert EN, et al. Occupational factors and risk of preterm birth in nurses. Am J Obstet Gynecol 2009;200;51.e1-51.e8.

    This study was supported in part by contract 200-2001-08007 from the Centers for Disease Control and Prevention and the National Institute for Occupational Safety and Health.

    The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health.

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