Pregnant women who work at least two night shifts in a single week could be at increased risk of suffering a miscarriage the following week, Danish researchers say today.
The research, published online in Occupational & Environmental Medicine, found that the risk could increase by as much as one third.
The authors accessed payroll data on 22,744 pregnant women working in Danish public services, mainly hospitals, and linked that with data from Danish national registers on births and admissions to hospital for miscarriage to determine how the risk of miscarriage between weeks 4-22 of pregnancy was influenced by night work.
The study included 377,896 pregnancy weeks – an average of 19.7 weeks per woman – and it was found that after week eight of pregnancy, women who had worked two or more night shifts the previous week had a 32% higher risk of miscarriage than those who had worked no night shifts.
The researchers also discovered that the risk of miscarriage increased with the number of night shifts worked per week and also by numbers of consecutive night shifts and that the risk was greater after week eight of pregnancy.
The authors write: “This may be explained by the decline in the proportion of chromosomally abnormal foetuses with gestational age, which makes an association with environmental exposure more easily detectable among later miscarriages.”
The underlying mechanism responsible for the association is that women working night shifts are exposed to light at night, which disrupts their circadian rhythm and decreases the release of melatonin, the researchers suggest. Melatonin has been shown to be important in maintaining a successful pregnancy, possibly by preserving the function of the placenta.
However, because this is an observational study, the authors stress they cannot establish the cause but say their findings are relevant because the “could have implications for national occupational health regulations."
Moelenberg Begtrup L, Olmer Specht I, Hammer P et al Night work and miscarriage: a Danish nationwide register-based cohort study. Occupational & Environmental Medicine 26 March 2019; doi:10.1136/oemed-2018-105592
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