Abstract
Background: An association between spontaneous abortions and shift work has been suggested, but present research results are conflicting. The aim of the study is to evaluate the relationship between spontaneous abortions among nurses, shift schedules, and nights worked. Methods: This is a longitudinal study where we identified 914 females from a cohort of nurses in Norway who had worked the same type of shift schedule 2008-2010; either permanent day shift, three-shift rotation or permanent night shift. Information on age, work and life-style factors, as well as spontaneous abortions during lifetime and the past three years (2008-2010) was obtained by annual questionnaires. Results: A higher prevalence of experienced spontaneous abortions before study start (2008) was found among nurses working permanent night shift compared to other nurses. In a linear regression analysis, a risk of 1.3 was found for experienced spontaneous abortions before study start among permanent night shift nurses, with day shift as reference, when adjusting for age, smoking, caffeine and job strain, but the finding was not statistical significant (95 per cent confidence interval 0.8-2.1). Permanent night shift workers had a risk of 1.5 experiencing spontaneous abortions in 2008-2010 compared to day shift nurses, although not statistical significant (95 per cent confidence interval 0.7-3.5). The number of night shifts the past three years was not associated with experiencing spontaneous abortions 2008-2010, but associated with a reduced risk of experiencing spontaneous abortions during lifetime. The results must be interpreted in the light of a possible selection bias; both selections into the occupation of nursing and into the different shift types of the more healthy persons may have occurred in this population. Conclusion: No significant increased risk of spontaneous abortion among permanent night shift nurses compared to day-time nurses was found in this study, and no association was found between spontaneous abortions and the number of worked night shifts.
Highlights
Reproductive health is an important issue for human beings
Most studies about shift work and spontaneous abortion (SA) have been performed among nurses, as this occupational group has the highest number of female shift workers in most countries
The baseline information showed that the nurses who worked permanent day shift were significantly older than the two other shift groups (Table 1)
Summary
Reproductive health is an important issue for human beings. In the past years, various occupational factors have been examined and suggested to be related to different reproductive outcomes of women [1,2]. Previous studies among nurses from various countries several years back in time have suggested a relationship between shift work and SA [3,4,5]. Some find SA to be related to work schedules with night shifts only [4,5], while others suggest a relation to rotating shift schedules that include nights [3,10] Several studies on this topic suffer from methodological limitations, such as a lack of prospective design, different and unclear definitions of shift work, and a lack of adjustment for confounding factors [6]. The aim of the study is to evaluate the relationship between spontaneous abortions among nurses, shift schedules, and nights worked
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