What happens when you give a mouse jet lag? If she's pregnant, the results could be disastrous. In a new study, researchers placed laboratory mice that had recently copulated on a regimen of artificial daylight. Then they shifted the rodents' exposure to this light forward by 6 hours every 5 to 6 days—the equivalent of flying from Chicago to London. Four time shifts later, only 22% of the mice gave birth, compared with 90% in a control group. Mothers may have reabsorbed their pregnancies, or fertilized eggs might never have implanted, the team reports online today in PLoS ONE. The result fits with previous studies which found that mice with mutations in genes that regulate their circadian rhythms, the body's timekeeper, have irregular estrous cycles and more pregnancy failures. Shift workers and flight attendants, whose own body clocks are disrupted, also report increased miscarriages and menstrual changes. But there may be hope. When mice were clock-shifted backward rather than forward, the effect was less severe. So even if circadian changes lead to fertility problems in women, careful scheduling might limit the turbulence.
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