The study concluded that an acute bout of HIIT exercise, as well as 30 minutes of moderate exercise, is well tolerated by both mother and fetus. Neither form of exercise negatively affected fetal heart rate or umbilical blood flow.

“The really important thing is that this is a first step where we’re identifying the potential safety and even potential benefits of HIIT exercise in pregnancy,” says lead researcher Dr Margie Davenport, director of the Program for Pregnancy and Postpartum Health at the University of Alberta, in Canada.

“Absolutely we need more studies, we need larger studies and we need chronic studies looking at continuing HIIT throughout pregnancy. But I do think that this begins to reduce the fear around engaging in HIIT exercise, because we know that pregnant women are still doing it.”

The study, which involved 15 women who were at least 20 weeks pregnant, included an HIIT session of 10 one-minute intervals interspersed with a one-minute rest, which saw the heart rate rise to 96 per cent of its maximum.

Current physical activity and exercise guidelines for pregnancy around the world strongly caution against engaging in vigorous exercise exceeding 80 to 90 per cent of one’s maximal heart rate, but this is owing to the paucity of information on fetal well-being.

At the time, Dr Amy Wang, a Hong Kong-based family doctor, repeated the recommendation that women should not engage in high-intensity activities and should stick to 30 minutes a day of moderate exercise.

But much less is known about vigorous exercise. The Canadian researchers were keen to explore this because this type of exercise takes up far less time.

The second-biggest barrier to exercise is time constraints, and currently only 15 per cent of pregnant women meet physical activity recommendations of 150 minutes of moderate exercise per week.

The researchers were also keen to explore HIIT as a time-saving alternative to moderate exercise while also addressing lack of knowledge or misinformation about maternal and fetal safety.

Despite the lack of scientific evidence to support the safety of vigorous exercise during pregnancy, an abundance of prenatal HIIT workouts and advice columns are being created and shared online.

“Our research was an opportunity to potentially identify a new form of training that can be continued safely during pregnancy. Now, the important thing to understand is the individuals in the study were relatively active,” says Davenport.

The research, published in the journal Sports Medicine, found that even though the HIIT session pushed women to beyond 96 per cent of their maximum heart rate – which is categorised as vigorous intensity exercise – it had no adverse effects.

A range of measures was recorded in the 15 participants, who were all at least 20 weeks pregnant. The study measured maternal heart rate, blood pressure, respiration, fetal heart rate and blood flow in the umbilical cord.

Concerns that too much blood flow could be redirected to the working muscle when pregnant women engage in vigorous exercises were shown to be unfounded.

“We didn’t see any slowing of the fetal heart rate. We actually saw some improvements in the blood flow to the baby, which is great,” says Davenport.