Time of day when labor is induced impacts how long labor lasts, study finds
Study shows that mothers induced during early morning had labors that were up to six hours shorter than those induced in late evening.
Mothers who need to have their labor induced — and especially those who are obese or are giving birth for the first time — could benefit from inductions that start in the early morning rather than later in the day.
“Time of induction has an effect on the length of labor,” said Rene Cortese, Ph.D., associate professor of pulmonary, critical care and sleep medicine at KU Medical Center.
Cortese, an epigeneticist who studies sleep and reproductive health and pregnancy, and Hanne Hoffman, Ph.D., a neurobiologist who studies circadian rhythm and reproductive physiology at Michigan State University, have published a study showing the impact of the timing of labor induction on labor duration. Their retrospective study analyzed more than 3,000 participants, who were at least 37 weeks pregnant, who underwent induction at a Michigan hospital between 2019 and 2022.
Their research found that the shortest induced labor durations occurred when the induction began between 3 a.m. and 9 a.m. The time of induction was defined as the time the initial dose of a synthetic version of the hormone oxytocin, which stimulates uterine contractions, or a cervical ripening agent was administered. Those induced during the early morning had labors up to six hours shorter than those who were induced in the late evening.
Participants in the study who were obese or having their first baby were found to be most susceptible to longer labor after induction. They were also the ones who benefited the most when induction started in the early morning.
associate professor of
pulmonary, critical care
and sleep medicine
at KU Medical Center
One-third of labors in the United States are now induced rather than contractions starting spontaneously, according to the Centers for Disease Control and Prevention. Common medical reasons include gestational diabetes, high blood pressure, infections in the uterus, labor that hasn’t started on its own well after the due date and problems with the baby. Labor is initiated medically to protect the health of the mother and baby, but induction typically also results in longer labor, sometimes even lasting a couple of days.
The study also showed that time of day also affected the rate of cesarean sections (inductions are associated with an increased risk of C-sections): The chances of having a cesarean delivery increased significantly when inductions started between 9 p.m. and midnight compared with inductions at other times.
“A C-section is a major surgery,” noted Hoffman. “And high BMI (body mass index), gestational diabetes, will make the recovery longer and at higher risk for infection and complications. So if you can reduce C-sections, that’s a huge win for the woman, her family, but also the healthcare system.”
Moreover, the time of induction did not have an effect on the baby’s health. “There was no negative impact to the baby — no increase to the admission rate to the NICU (neonatal intensive care unit), no increase in diagnosed respiratory distress, all the complications that could happen perinatally, which is very important,” said Cortese.
More studies are needed before these findings could be applied to clinical practice guidelines, the researchers stressed. Future studies also will focus on the biological mechanisms that drive labor and how, for example, variations in circadian clocks, such as those caused by a higher body mass index, affect the body’s response to oxytocin and uterine contractions.
This is not the first study to explore the connection between induction timing and labor duration, the researchers noted, but most studies look at time simply in terms of day versus night. It is well established that spontaneous labor and birth peak during late evening and early morning, indicating that circadian mechanisms, which are biological clocks in cells that control the body’s processes, contribute to the onset of labor. But the timing of induction of labor has not been thoroughly considered, and Cortese and Hoffman wanted to take a more granular look.
“We’re showing a very simple change in the management (of labor) that (could) really impact the way that delivery works,” said Cortese.