Pregnant women who work at least two night shifts in one week may have a heightened risk of miscarriage the following week. Lead author Dr. Luise Molenberg Begtrup explained in an email that "women working night shifts are exposed to light at night which disrupts their 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." According to Reuters, Begtrup, a researcher in the department of occupational and environmental medicine at Bispebjerg and Frederiksberg Hospital in Copenhagen, and her colleagues analyzed pregnancy outcomes in 22,744 public service workers, most of whom were employed in Danish hospitals. Among the 10,047 women in the study who had done some night shift work during weeks three through 21 of their pregnancies, there were 740 miscarriages. The researchers wrote in the journal Occupational & Environmental Medicine. Among the 12,697 women who did no night shift work, there were 1,149 miscarriages. After accounting for maternal age, body mass index, smoking, number of previous births, socioeconomic status and former miscarriages, researchers found that working two or more nights in a single week between weeks eight and 22 was associated with a 32 percent increased risk of miscarriage in the following week. Dr. Zev Williams, chief of reproductive endocrinology and infertility at Irving Medical Center of Columbia University, New York, sees that while the researchers have found an association, it’s not proof that night shift work causes miscarriage, adding that "This was not a randomized trial. With something like this, there are so many other confounders."