Women who work two or more night shifts in one week may have a greater risk of miscarriage the following week, according to Danish researchers.
This work pattern may increase a pregnant woman’s risk of miscarriage the following week by around a third, suggests a study published in the journal Occupational & Environmental Medicine.
“The results could have implications for national occupational health regulations”
Previous studies have suggested that pregnant women face a greater risk of miscarriage if they work night shifts.
However, they have been based on self-reported shift work and have not quantified the level of increased risk or the amount of shift work involved.
For this study, the authors accessed payroll data on 22,744 pregnant women working in public services, mainly hospitals, in Denmark.
They compared it with data from Danish national registers on births and admissions to determine how the risk of miscarriage between weeks four and 22 of pregnancy was influenced by night work.
Overall, 377,896 pregnancy weeks were included – an average of 19.7 weeks per woman – noted the researchers.
After week eight of pregnancy, women who had worked two or more night shifts the previous week had a 32% higher risk of miscarriage compared with those who had not worked any night shifts that week.
In addition, the risk of miscarriage increased with the number of night shifts worked per week and also by numbers of consecutive night shifts.
The association between night work and the risk of miscarriages was stronger after pregnancy week eight, said the study authors from the Bispebjerg and Frederiksberg Hospital in Copenhagen.
“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,” they said.
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As around 14% of women in Europe report working at night at least once a month, the findings have relevance for pregnant women as well as their employers, physicians and midwives, they noted.
“Moreover, the results could have implications for national occupational health regulations,” added the study authors.
In terms of the underlying mechanism responsible for the association, women working night shifts are exposed to light at night that disrupts the circadian rhythm and decreases the release of melatonin.
Melatonin has been shown to be important in maintaining a successful pregnancy, possibly by preserving the function of the placenta.