“Clocks appear in all the tissues of our bodies,” Varcoe explains. “Rhythmic clock genes are expressed in pregnant and non-pregnant uteri, but we don’t really know what they do. There are many other factors that a fetus gets exposed to, including hormonal rhythms from the mother.”
So should a pregnant mother quit working the night shift, or stop flying cross-country? Not so fast: it’s not easy to translate results from animal models into medical advice for people, says Michael Katz, a doctor who works for March of Dimes (which helped to fund the study). Human and mouse reproductive cycles are similar—both species have estrous cycles that are guided by the circadian clock—but there are subtle differences. Mouse estrous cycles last only four days, for example, and mice do not menstruate.
Nevertheless, the results suggest that “if a woman is working at unusual hours, and is trying to get pregnant and can’t, perhaps this is something she should look into,” Katz says. He says that women can still work night shifts and have healthy pregnancies-- the main thing is to be consistent.
Summa agrees. “What we can suggest,” he says, “is that for women who are trying to conceive, it’s probably beneficial to maintain good sleep cycles. They should go to sleep at about the same time every day, and get plenty of sleep.” And because circadian disruptions have been linked to many health problems—including obesity and diabetes, bipolar behaviors, and depression—that may be good medical advice for everyone.