From Scientific American:
“My biological clock is ticking.” The phrase typically pops up in movies about middle-aged women who want to start a family before menopause makes it impossible. But a new study published May 23 in PLoS ONE indicates that another clock may also be important for females trying to conceive: the one that regulates our waking and sleeping cycles.
A strong body of evidence links daily wake-sleep cycles to feminine reproductive cycles. When scientists remove a female mouse’s suprachiasmatic nucleus—the pacemaker in her brain that regulates daily circadian rhythms—her estrous cycle ceases, and she becomes infertile. In human females, working night shifts and frequently traveling across time zones has been associated with menstrual irregularities, reduced fertility and a greater number of negative pregnancy outcomes such as low birth weight, preterm birth and miscarriage. But “one of the issues with these epidemiological studies,” says Keith Summa, a medical and doctoral student at Northwestern University, “is that there are other factors associated with shift work that may also be playing a role.” For example, women who work night shifts also tend to sleep less. “Our study provides stronger evidence that reproductive problems are due to circadian disruption itself,” Summa says.