Researchers at Washington University in St. Louis reported on Apr. 11 that a mother's internal clock helps set the biological clock for her babies while they are still developing in the womb, according to a new study published in the Journal of Biological Rhythms.
Understanding how and when circadian rhythms begin is important because disruptions to these daily cycles have been linked to long-term health problems. The study's findings may help inform medical treatments and public health policies regarding pregnancy care.
The scientists developed a method using genetically engineered mice with a luminescent protein attached to their clock proteins, allowing them to observe circadian activity in fetuses inside the womb. By tracking light produced by this protein, researchers identified clear cyclical patterns of clock gene expression in developing pups.
"We found clear day-night rhythms in the pups that synchronized to the mother's rest-activity cycle during the last week of pregnancy, equivalent to the third trimester in humans," Lokesh said. "This suggests that the clock machinery forms early in development and receives entraining cues from mom later."
Erik Herzog, Viktor Hamburger Distinguished Professor of biology and senior author on the study, said: "Importantly, we found daily rhythms across the placenta from the mother to the baby before the fetus can sense light." The synchronization was linked with glucocorticoid hormones crossing from mother to fetus through the placenta.
The authors noted that synthetic glucocorticoids are often given to pregnant women at risk of preterm birth without considering natural hormone fluctuations throughout the day. They found administering these steroids daily accelerated synchronization of fetal circadian rhythms.
Researchers also observed an association between failure to develop circadian gene activity and failure of delivery but cautioned more research is needed: "We cannot yet say whether absence of rhythms contributes to developmental problems or simply reflects them," Lokesh said.
Lokesh emphasized maintaining stable circadian rhythms during pregnancy due to widespread exposure to artificial light at night worldwide. He added: "Understanding when and how the body clock starts ticking helps scientists identify sensitive developmental windows when circadian disruption may have lasting effects... This knowledge could help guide medical treatments, inform clinical practices and shape public health policies aimed at protecting neonatal circadian health during pregnancy."
