Pregnant women who work two or more night shifts in a week are at higher risk for miscarriage the following week, a new study revealed.

Researchers in Denmark found that women who work at night are exposed to light that disrupts their circadian rhythm and decreases the release of melatonin, which is important in a successful pregnancy because it preserves the placenta.

However, other experts dismiss the findings of the study because it is "not strong enough for people to think they need to change their lifestyles."

Night Shift Is Linked To Miscarriages

The team of researchers analyzed pregnancy outcomes among 22,744 public service workers, most of whom worked in hospitals in Denmark.

They matched records from these workers with those of women from the Danish Medical Birth Register, which provided researchers information on pregnancies that resulted in births as well as from the Danish National Patient Register, which provided information on miscarriages.

The study revealed that among 10,047 women who went on night shift during the third week to the 21st week of their pregnancies, 740 women had miscarriages.

Meanwhile, among 12,697 women who did not go on night shift, 1,149 women had miscarriages.

Taking into account the age of the mother, body mass index, smoking habits, number of previous births, socioeconomic statuses, and former miscarriages, the study found that working two or more night shifts in a single week between the 8th week and 22nd week of pregnancy was linked to a 32 percent increased risk of miscarriage in the next week.

Pregnant women who worked 26 or more graveyard shifts between the fourth week and 22nd week were more than twice as likely to have a miscarriage compared to those who worked no night shifts. This finding was based on eight women, researchers said.

What Are The Impacts Of This Study?

The study above is based on observational research, which means it does not establish cause. Other experts believe it is no proof that working night shift causes miscarriages. What's more, data regarding miscarriages were incomplete, the researchers said.

"This was not a randomized trial. With something like this, there are so many other confounders," said Dr. Zev Williams, who works at NewYork-Presbyterian/Columbia University Irving Medical Center.

This means that there must be other factors that affected the health of the night shift workers and the study did not take those factors into account.

Williams said the results of the data is not enough to convince pregnant women to change their lifestyles. He explained that in an individual case, the risk is so small and that preventing pregnant women from working night shifts will not have a major effect on reducing the rates of miscarriages.

Still, the findings of the study are helpful for the 14 percent of women in Europe who work night shifts every day.

Dr. Luise Molenberg Begtrup, lead author of the Denmark study and a researcher in the occupational and environmental medicine department at Bispebjerg and Frederiksberg Hospital in Copenhagen, said the results of the study can have implications for national occupational health regulations.

The details of the study are published in the journal BMJ.

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