Even though women are often advised to steer clear of certain yoga poses late in pregnancy, many of these moves might not be a problem for women or their babies, a small U.S. study suggests.
Yoga can have many benefits during pregnancy, including helping women maintain flexibility and muscle tone and develop breathing techniques that may be useful during labor. But late in pregnancy women are often warned against poses that require them to lie on their backs, such as "happy baby pose" or "corpse pose," and inversions such as "downward facing dog" that might reduce circulation to the fetus and contribute to a spike in fetal heart rate.
To see how much caution might be warranted, researchers monitored fetal heart rate while a group of 25 healthy women in the final weeks of pregnancy tried 26 common yoga poses.
Fetal heart rate remained normal through all of the poses, and none of the women reported decreased fetal movement, contractions, fluid leakage or vaginal bleeding in the 24 hours after their yoga sessions, researchers report in the journal Obstetrics and Gynecology.
"Though this is a preliminary study, I found there were no adverse changes in maternal or fetal wellbeing in the 26 studied poses," said lead author Rachael Polis, who conducted the research at Jersey Shore University Medical Center and is currently with Kosair Children's Hospital Gynecology Specialists in Louisville, Kentucky.
"Postures suspected to be contraindicated - e.g. downward facing dog, child's pose, happy baby and corpse pose - were also well tolerated," Polis added by email.
None of the women in the study had a history of hypertension or other complications during pregnancy, and none of them had any medical conditions that required them to avoid exercise.
The women were near the end of their third trimester, at about 35 to 37 weeks pregnant. Ten of the 25 participants did yoga regularly, while eight were familiar with yoga and seven had never done it before.
Each woman completed a one-on-one yoga session with a certified yoga instructor, with an obstetrician and a medical resident in the room. They had stress tests before going through the poses and again afterward.
Given the size of their bellies, they didn't do any yoga poses lying on their stomachs. They also avoided complete inverted poses such as hand stands or head stands. To avoid falls or other injuries, they could modify poses by using blocks, chairs or the wall for support.
Beyond the small size of the study, other limitations include yoga sessions that might not match the duration or intensity of a typical community yoga class, the authors concede. The women in the study were typically of a normal healthy weight, too, while more than half of pregnant women tend to be overweight or obese.
It's also possible that women might encounter poses not covered by this experiment that could cause problems during pregnancy, noted Kathryn Curtis, a researcher at York University in Toronto who wasn't involved in the study.
"I encourage pregnant women to seek out studios that offer specialized prenatal yoga classes that are taught by teachers who have prenatal yoga training," Curtis said by email.
"Women should practice hatha based, restorative practices with breath awareness components, rather than heated or strength focused practices, for safety precautions for both the mother and baby," Curtis added.
In a separate study reported in the American Journal of Obstetrics and Gynecology, 52 pregnant women who had never tried yoga were randomly assigned to either participate in a one-time, one-hour yoga class, or to attend a one-time, one-hour PowerPoint presentation about exercise, nutrition, and obesity in pregnancy.
In this study too, there was no significant change in fetal blood flow immediately after the moms did yoga, according to Dr. Shilpa Babbar of the University of Missouri Kansas City and colleagues.
"Yoga can be recommended for low risk women to begin during pregnancy," Babbar's team concluded.