New European research has found that pregnant women who work more than two night shifts in a week may have a greater risk of miscarriage the following week.
Carried out by Danish researchers, the new study looked at payroll data gathered from 22,744 pregnant women working in public services, mainly hospitals, in Denmark.
The information was then linked with data taken from Danish national registers on births and admissions to hospital for miscarriage, to calculate how night shift work might affect the risk of miscarriage between weeks four to 22 of pregnancy.
The findings, published online in Occupational & Environmental Medicine, showed 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 compared with women who had not worked any night shifts that week.
Moreover, the risk of miscarriage increased with the number of night shifts worked per week, and also by numbers of consecutive night shifts.
As an observational study, the researchers point out that they cannot establish causal effect. They also note that the data on miscarriages was incomplete.
However, the study is the first to investigate the association between night work and miscarriage risk using a detailed measurement of night work among participants.
Although previous studies have also suggested that the risk of miscarriage is higher for pregnant women who work night shifts, these studies were based on self-reports by women, which can be susceptible to inaccuracies.
The researchers also added that the new findings are important given that around 14% of women in Europe report working at night at least once a month.
As to the reasons why night shift could increase the risk of miscarriage, the researchers point out that previous studies have found that melatonin, the hormone which makes us feel sleepy, is important for maintaining a successful pregnancy, possibly by helping preserve the placenta.
Working night shifts, however, exposes us to light at night which can disrupt the circadian rhythm and decreases the release of melatonin.