April 30, 2019

Pregnancy causes changes in daily rhythms and activity level beginning in the first trimester in both mice and women, which normally resolve shortly before term delivery, according to a new study from the March of Dimes Prematurity Research Center at the University of Washington School of Medicine, published in Journal of Biological Rhythms. March of Dimes is the leading nonprofit for the health of moms and babies.

“This finding is fascinating because while we know that miscarriage, preterm birth, and other serious complications during pregnancy are linked to disruptions in a mom’s circadian rhythm, we don’t know how it works,” says Kelle H. Moley, MD, Senior Vice President and Chief Scientific Officer for March of Dimes. “This study takes us one step closer to understanding how normal circadian rhythm supports healthy pregnancy.” 

Circadian rhythms (the body’s 24-hour internal clock), which involve sleep/wake cycles, metabolism, hormone secretion, activity level, and other physical processes, influence reproduction in many species, including humans. Chronotype is the propensity for an individual to sleep at a particular time during a 24-hour period. Disturbances to these processes known as chronodisruption can be caused by factors such as shift work, time-zone travel, or clock gene mutations, and are associated with poor reproductive outcomes.

“Our observations of the normal advances in chronotype during pregnancy may explain why late chronotype pregnant women are about 2.5 times more likely to develop gestational diabetes in their second trimester than were those who had an earlier chronotype,” wrote the team of authors led by Carmel A. Martin-Fairey, PhD and Erik D. Herzog, PhD. They also note that previous studies have shown women who work at night or on rotating shifts are 60 percent more likely to miscarry or deliver preterm than women who work day shifts.

The researchers also noted that the decreased levels of activity during late pregnancy in mice and throughout pregnancy in women are consistent with a large body of literature and suggest a conserved mechanism that modulates sleep/wake cycles during pregnancy in both species. 

“Pregnancy Induces an Earlier Chronotype in Both Mice and Women” by Carmel Martin-Fairey, Erik Herzog, Sarah England, Justin Fay, and Emily Jungheim, et. al., was first published online April 24 in Journal of Biological Rhythms,