Night shift and pregnancy loss

Pregnant women who regularly work the night shift may have an increased risk of a miscarriage late in pregnancy or a stillbirth.Researchers from the University of Aarhus, Denmark, studied more than 40,000 women who worked during pregnancy and found that those who consistently worked the night shift were 85 percent more likely than daytime workers to suffer a miscarriage, relatively late in pregnancy or have a stillbirth. Other job shifts - including rotating shifts that required some overnight work - were not related to late pregnancy loss. Overall, just over 1 percent of the pregnancies ended in miscarriage or stillbirth, and only 11 of the 420 women who worked a fixed night shift suffered a pregnancy loss. Still, when the researchers weighed other factors such as the woman's age, smoking habits and the physical demands of the job, overnight work was linked to an 85 percent higher risk of pregnancy loss compared with fixed daytime work. The findings are in line with a number of other studies suggesting that working the late shift, or rotating shifts that include night work, can take a toll on the body, including increasing the risk of digestive problems, heart disease and certain cancers. The researchers found that those who worked nights or rotating shifts had a slightly higher risk of having a low-birth-weight baby.

It is thought that night-time work may promote health problems by throwing off the body's circadian rhythms - daily physiological patterns, governed by the body's internal clock, that not only help control the sleep/wake cycle, but also influence a range of body processes, including blood pressure changes and hormone production. The link between pregnancy loss and steady overnight work may be linked with oestrogen levels, the researchers hypothesised. Exposure to light at night suppresses the normal nighttime release of the sleep-related hormone melatonin, which in turn is believed to spur an increase in other hormones, including oestrogen. The researchers also found evidence that job stress could be a factor in night-shift workers' higher risk of miscarriage and stillbirth. Job stress was not linked to pregnancy loss overall, but among workers on fixed night shifts, those who felt their jobs had high demands and gave them little control over their work had a higher risk of pregnancy loss.

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