I know what you’re thinking: Who needs more mice? Actually, this result could also be of importance for humans who seek to have children. Keith Summa, Martha Vitaterna and Fred Turek from Northwestern University have shown that major disruptions in day/night cycles are associated with dramatic decreases in successful pregnancies, at least for mice.
The researchers divided newly pregnant mice into three groups. One group (control) lived in a constant and uniform cycle of twelve hours light, twelve hours dark. The second group (phase-delayed) had their lights go on six hours later every five to six days, and the final group (phase-advanced) had reveille six hours earlier every five to six days. This means that the ‘daylight’ hours of the latter two groups had been shifted completely around the clock by the time they gave birth three weeks after conception.
Mice in the control group went on to successfully have pups 90% of the time. In contrast, the phase-delayed and phase-advanced groups had babies only 50% and 22% respectively. Like most humans, mice apparently find getting less sleep more troubling than getting more sleep.
Previous studies have shown a correlation between circadian rhythms and the ability to conceive. This new data shows that rapid shifting of the day/night schedule can also affect pregnancy outcomes after conception. Keep in mind that this study only involved 48 mice and that results from mouse studies don’t always apply to humans. Still, if you are attempting to have a child, you might consider avoiding shift-work if you can.
For a fascinating discussion of circadian rhythms, don’t miss Ed Yong’s post here.