Earlier studies showed that pregnant women are at a higher risk of miscarriage if they work night shifts. However, these studies were based on self-reported shift work and did not quantify the level of increased risk or the amount of shift work involved.
Therefore, for the current study, the researchers examined data of 22,744 pregnant women working in public services, mostly hospitals, in Denmark. Then, they associated that data from Danish national registers on births and admissions to hospitals for a miscarriage to know how night work influences the risk of miscarriage between weeks four to 22 of pregnancy. Overall, the researchers included 377,896 pregnancy weeks, with an average of 19.7 weeks per woman.
The researchers found that after the eighth week of pregnancy, women who had worked two or more night shifts on the previous week were 32 percent more likely to have a miscarriage than those who had not worked any night shifts on the same week. The risk of miscarriage increased with the number of night shifts worked per week as well as by numbers of consecutive night shifts. Moreover, they found that the risk of miscarriages increased after the eighth week of pregnancy.
"This may be explained by the decline in the proportion of chromosomally abnormal fetuses with gestational age, which makes an association with environmental exposure more easily detectable among later miscarriages," explained the researchers.
The researchers also posited that the reason behind this link may be because women working night shifts are exposed to light at night, which interrupts their circadian rhythm and reduces the levels of melatonin. Melatonin is a sleep hormone and is important in maintaining a successful pregnancy by preserving the function of the placenta. (Related: Decreased melatonin disrupts the body clock and increases cancer risk: Night workers found to have highest risk.)
The researchers noted that their paper was an observational study, so they couldn't establish a cause. They also pointed out that data on miscarriages, particularly early miscarriages, were incomplete. Nonetheless, they believed that their findings were important as many pregnant women are working at night at least once a month. Their findings could also have implications for national occupational health regulations.
What should pregnant women do if they work at night?
For some pregnant women, working at night may be their only option. Health experts suggest several ways for pregnant women to ensure that they remain healthy during pregnancy.
Pregnant women must maintain a regular sleeping schedule as much as possible and avoid alternating day shifts and night shifts. Having a fixed night shift schedule is better and may be less stressful on the body than working on alternating shifts. However, it is important to note that daytime sleep can be lighter, shorter and of poorer quality than sleep at night because of light, noise and temperature.
Pregnant women should also maintain a healthy weight and watch what they eat. Night shift workers, in general, tend to become overweight or obese because of an unhealthy diet and the disruption of their body clocks. They should also have routine obstetrical visits and control their pre-existing medical conditions, such as diabetes or hypertension.
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