Department of Occupational and Environmental Medicine, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark.
The Parker Institute, Bispebjerg and Frederiksberg Hospital, Frederiksberg, Denmark.
PLoS One. 2019 Apr 18;14(4):e0215748. doi: 10.1371/journal.pone.0215748. eCollection 2019.
Melatonin stimulates the production of progesterone, which is essential for the maintenance of pregnancy. Since melatonin in blood is reduced due to work under illuminated conditions during night work, it has been hypothesized that night work may increase the risk of preterm birth. Previous meta-analyses have not revealed increased risk of preterm birth in women working night shifts during pregnancy. Still, these studies might have been limited by inaccurate self-reports of timing, intensity and duration of night work most likely causing bias towards the null. The aim of this is study was to investigate if the frequency and duration of night work during the first (week 1-12) and second (week 13-22) trimester of pregnancy were associated with risk of preterm birth when objective and prospective data on night work are used.
In a register-based prospective cohort study, we obtained individual day-to-day information on working hours from The Danish Working Hour Database (DWHD, a payroll database including all public service employees in administrative Danish Regions from 2007-2013) and information on preterm birth from the Danish Medical Birth Registry. Night-shift was defined as at least three working hours between 23:00 and 06:00. Preterm birth was defined as giving birth during gestational weeks 23-37. Odds of preterm birth according to working night shifts were analysed by logistic regression.
We identified 16,501 pregnant women eligible for the study, of which 10,202 women (61.8%) had at least one night-shift during the first 22 gestational weeks. The risk of preterm birth was not elevated among women working night shifts compared to women working only day shifts during either the first or second trimester. Within night-shift workers, the risk was not related to the number of night shifts, the duration of night shifts, consecutive night shifts or quick returns defined as short intervals between shifts. Odds of preterm birth was not related to change of working schedule from the first to second trimester, although women changing from night shifts in the first trimester to day work only in the second trimester displayed a weak increased odds of preterm birth (OR 1.21, 95%CI 0.98-1.49) compared to women working night shifts in both trimesters.
Our results, which are without bias from self-report of either exposure or outcome, are in line with the results of previous meta-analyses. Due to the detailed information on hours worked during pregnancy, we were able to investigate several dimensions of night work not previously investigated, of which none were associated with elevated risk of preterm birth.
褪黑素可刺激孕激素的产生，而孕激素对于妊娠的维持至关重要。由于夜班工作期间，人体在夜间处于光照环境下，会导致血液中的褪黑素减少，因此人们推测夜班工作可能会增加早产的风险。先前的荟萃分析并未显示出孕妇上夜班与早产风险增加之间存在关联。然而，这些研究可能受到自我报告的时间、强度和夜班持续时间不准确的限制，这很可能导致结果偏向于无效。本研究旨在探讨当使用客观和前瞻性的夜班工作数据时，妊娠第一（第 1-12 周）和第二（第 13-22 周）孕期中夜班工作的频率和持续时间是否与早产风险相关。
在一项基于登记的前瞻性队列研究中，我们从丹麦工时数据库（DWHD，一个包含了 2007-2013 年期间所有丹麦行政区域的公共服务员工的工资数据库）中获得了关于工作日的逐天信息，并从丹麦医疗出生登记处获得了早产信息。夜班被定义为至少 3 小时的工作时间在 23:00 至 06:00 之间。早产定义为在妊娠 23-37 周时分娩。通过逻辑回归分析了夜班工作与早产之间的关系。
我们确定了 16501 名符合研究条件的孕妇，其中 10202 名（61.8%）孕妇在妊娠的前 22 周至少有一次夜班。与仅上白班的孕妇相比，上夜班的孕妇早产的风险并没有增加。在夜班工人中，夜班的次数、夜班的持续时间、连续夜班或快速倒班（定义为班次之间的短间隔）与早产风险无关。从第一到第二孕期工作时间的变化与早产风险无关，尽管从第一孕期转为仅第二孕期上白班的女性早产的几率略有增加（OR 1.21，95%CI 0.98-1.49）与两个孕期都上夜班的女性相比。
我们的结果没有自我报告的暴露或结果的偏倚，与之前的荟萃分析结果一致。由于我们有关于怀孕期间工作时间的详细信息，我们能够调查以前没有调查过的夜班工作的几个维度，其中没有一个与早产风险增加有关。
