A respected Canadian research team is warning expectant mothers to stay away from hugely popular hot yoga classes early in their pregnancy.
Practised in studios heated to up to 40 degrees Celsius, hot yoga exposes pregnant women and their fetuses to excessive heat. Excessive core body temperatures, in turn, can cause maternal hyperthermia, which, in the first trimester of pregnancy, has been shown in animals and humans to increase the risk of neural tube defects — malformations of the brain and spine, including spina bifida.
“With the increased risk of neural tube defects and possibly of other malformations among fetuses exposed to excessive heat, pregnant women should avoid practising hot yoga during pregnancy,” researchers with the Motherisk program at Toronto’s Hospital for Sick Children write in the latest edition of the journal, Canadian Family Physician.
Last month the same team calmed fears over the use of Botox during pregnancy.
Hot yoga, they say, is a different story.
One popular form of hot yoga, Bikram yoga is practised at temperatures of 35 to 40 degrees Celsius. But no published studies yet exit “on the safety and outcomes of this form of yoga for pregnant women and their fetuses,” the researchers said.
“Moreover, there is a lack of consensus among yoga clubs about allowing pregnant women into hot yoga classes,” they said. “This is a concern because hyperthermia is a known environmental teratogen (something that can change the normal growth of a fetus) in both animal models and humans.”
In 2005, the Motherisk team reported that their review and analysis of published studies found that pregnant women who developed hyperthermia from prolonged fevers or from external heat sources such as hot tubs, saunas and electric blankets had a two-fold increased risk of neural tube defects.
“Women may not be aware that a high temperature may not be good for her baby,” said Dr. Gideon Koren, director of Motherisk and the leading author.
Neural tube defects occur early in pregnancy. The embryo forms a brain and spinal cord by essentially folding a flat portion of embryo into a tube.
If the tube doesn’t completely close, the result can be either spina bifida, which can cause paralysis, or anencephaly, a devastating defect in which a baby is born with parts of the brain and skull missing.
This neural tube rolling up and closing is completed by the 28th day of pregnancy. It’s possible that a high body temperature may disrupt that process, Koren said.
Two recent reviews suggest that yoga in pregnancy can lower stress, pain and anxiety and improve sleep. “Yoga, per se, is not the issue,” Koren stressed. “It’s the heat (newly pregnant women) should avoid.”
He recommends women avoid hot yoga during their first trimester of pregnancy. Hot yoga is safer in the second and third trimester unless the woman has other restrictions related to heat exposure, he said, such as low or high blood pressure, fatigue, a chronic illness or severe morning sickness.
Claire Cameron, owner of Bikram Yoga Ottawa, said that regular students who have practised Bikram yoga for more than a year could continue practising if they become pregnant, but only after their first trimester. “We’re super cautious about it,” Cameron said. Pregnant women are also taught special positions that eliminate forward bends or postures that compress the stomach.
Cameron said it’s common for women to miscarry in the first trimester, “and, just to be safe, you don’t want people blaming the yoga.”
But, “I’m not sure why the doctors say an increased body temperature is bad,” she said. “What about the people who live near the Equator, or people in India? The temperature of a hot yoga studio is no hotter than Ottawa in summer.”
In addition to the increased risk of neural tube defects, excessive heat exposure might cause dizziness or fainting because blood pressure tends to be lower in the first trimester of pregnancy, Koren’s group writes.