March 25, 2019

expert reaction to night shifts and miscarriage

Research published in Occupational & Environmental Medicine corroborates earlier findings that night work during pregnancy may confer an increased risk of miscarriage.

Dr Yvette Martyn, Occupational Health Physician at Medigold Health, said:

“This piece of research was performed in Denmark and the participants were mostly nurses and doctors who were pregnant between 2007-2013. The researchers found that working two or more night shifts the previous week, would increase the risk of a miscarriage by 32%, this was based on 102 miscarriages occurring in 21,099 pregnancy weeks for women in this category compared to 780 miscarriages out of 225,282 pregnancy weeks for women in the no night shift group.  A pregnancy week is one woman being pregnant for one week while involved in the study.  If a woman is pregnant and in the study for 10 weeks, then that would contribute 10 pregnancy weeks to the study.

“The strengths of this study are that the researchers had access to a database which provided clear information on who had worked certain shifts, in other studies the participants may have issues with recalling which shifts they had worked.  There are also a large number of participants included in the study, 22,744 people.

“There are a number of limitations in relation to this study. The study authors were not aware of if the workers were lifting during their shifts or if they were in non-sitting postures, and these factors can increase the risk of miscarriage.  A previous study has indicated that nurses on day shifts perform less strenuous work than those working during the night. The researchers were only able to pick up miscarriages if women had been treated in hospital as opposed to those treated in primary care.  The study authors have also stated that there was a difference in the distribution of the socioeconomic status, occupations, number of previous pregnancies and number of previous miscarriages between those working nights and those who were not working night shifts, and these factors could have the potential to influence the results.

“This is an observational study so it cannot establish if night shifts cause miscarriages.  In relation to protecting the health of pregnant women who work night shifts as part of their job, in the UK the Health and Safety Executive state that: “a new or expectant mother may work nights, provided this presents no risk to her health and safety. However, if a specific work risk has been identified – or her GP / midwife has provided a medical certificate stating she must not work nights – her employer must offer suitable alternative day work, on the same terms and conditions. If that is not possible, the employer must suspend her from work on paid leave for as long as is necessary to protect her health and safety and / or that of her child.””

Dr Jane Stewart, Chair of the British Fertility Society, said:

“This is an interesting paper looking to understand the association of miscarriage and night shift working. In the population studied, night shift exposure in early pregnancy is associated with a higher risk. This does not tell us that it is the cause but may add to the discussion around health and wellbeing in early pregnancy and the need to consider occupational health also.”

‘Night work and miscarriage: a Danish nationwide register-based cohort study’ by Luise Moelenberg Begtrup et al. was published in Occupational & Environmental Medicine at 23.30 hours UK time Monday 25 March 2019.

Declared interests

Dr Martyn: I am on the editorial board for the journal Occupational Medicine