When pregnant women go a week or more past their due date, doctors can either choose to induce labor or take a "wait-and-see" approach. A new study finds that it is safer for the baby if doctors induce labor in pregnant women at 41 weeks.
The results of the clinical trial were so startling the researchers stopped it early after six babies died because they thought it would be unethical to continue.
In the study, Swedish researchers followed nearly 3,000 pregnant women, who were randomly assigned to be induced at 41 weeks or “expectantly managed” till week 42. Inducing labor occurs when a pregnant woman is given medication or by other methods, such as breaking the amniotic sac.
“A policy of induction of labor at 41 gestational weeks instead of waiting until 42 gestational weeks is associated with fewer deaths of babies, without an increase in cesarean delivery or maternal complications,” the study’s lead author, Dr. Ulla-Britt Wennerholm, an associate professor and senior consultant in the department of obstetrics and gynecology at Gothenburg University, said.
Wennerholm was quick to reassure pregnant women that even when doctors postpone induction, “the absolute risk for the baby to die before or shortly after birth after 41 gestational weeks is very small — less than 0.5 percent.”
Why does stillbirth happen?
The researchers don’t know exactly why stillbirth is more likely to occur after 41 weeks, although risk factors may include placental disorders and dysfunction, delayed fetal growth, umbilical cord complications or infections.
For the study, women who were experiencing uncomplicated singleton pregnancies were recruited from 14 Swedish hospitals between 2016 and 2018. The women, whose average age was 31, were randomly assigned to be induced at 41 weeks or expectantly managed for the next week, at which time they would be induced if they had not yet delivered on their own.
We’ve known for years that when a pregnancy reaches a certain gestational age the risk of stillbirth goes up.
While the two groups did not differ much in terms of overall pregnancy complications and deaths, six babies in the wait-and-see group died, compared to none in the group who were induced. Although the researchers had planned on running the study for at least another three years, the trial was ended because of the rate of stillbirths in the wait-and-see group, Wennerholm said.
In other words, based on the findings, for every 230 pregnant women induced at 41 weeks, one perinatal death would be prevented.
Only about 6% of babies in the U.S. were born in week 41 and less than 1% at 42 weeks, according to 2017 data from the Centers for Disease Control and Prevention.
Dr. William Grobman, a professor of obstetrics and gynecology at Northwestern University’s Feinberg School of Medicine, said the new study is important because it helps dispel some misapprehensions that are prevalent among both doctors and mothers-to-be.
Some earlier observational studies suggested induction was associated with an increase in C-sections, but in recent years, four large trials looking at inducing at a specific gestational age have shown a "lack of maternal harm and a lack of perinatal harm,” Grobman said. “And in each of them there has been some evidence of benefit to both woman and child.”
The goals of the obstetrician and the pregnant women must be aligned — safe mother and safe baby.
With respect to the risk of stillbirth, Grobman said, “we’ve known for years that when a pregnancy reaches a certain gestational age the risk of stillbirth goes up. In fact, at week 39 it begins to rise and it really takes off after 41 weeks.”
While it’s not known just why that is, “we know that over time the placenta begins to function less well,” Grobman said.
At the University of California, Los Angeles, doctors and patients decide together what to do if the pregnancy goes past the due date, said Dr. Yalda Afshar, an assistant professor in the department of maternal fetal medicine at UCLA Health. “The goals of the obstetrician and the pregnant women must be aligned — safe mother and safe baby,” she said.
The new research will help “strengthen our recommendation for delivery before 42 weeks’ gestation,” Afshar said in an email. “This type of study is the absolute ‘gold standard’ of how we evaluate medical recommendations and decision making.”
The study was published Thursday in the BMJ.