Safely Exercising while Pregnant

In recent years, medical experts have recommended that pregnant women regularly exercise. Pregnant women have responded enthusiastically and creatively, adapting many standard workouts to fit their quickly changing bodies and physiological needs. Indoor cycling has become a favourite workout in later months of pregnancy, as it eliminates the balance issues and fear of crashing associated with outdoor cycling.

The explosion of smart trainers and virtual group workouts has made indoor cycling even more appealing. For example, Zwift has created a Baby on Board workout collection that is specifically designed for pregnant women. Created by Olympic gold medalists Kristin Armstrong and Dani Rowe, the training plan focuses on shorter, less-intense workouts that are designed to be safe for mothers and their babies. 

The American College of Obstetricians and Gynecologists (ACOG) provides extensive, easy-to-read advice for exercising while pregnant.It reports, “Physical activity and exercise in pregnancy are associated with minimal risks and have been shown to benefit most women, although some modification to exercise routines may be necessary because of normal anatomic and physiologic changes and fetal requirements.”  

This is great news for women who want to maintain their healthy lifestyle throughout pregnancy. But what are the workout modifications needed to avoid risk?  

Overheating is a danger 

One concern of exercising while pregnant is overheating. Risks to the fetus can occur when the mother's temperature rises more than 2.0°C above baseline (which is commonly described as reaching a temperature higher than 39°C/102°F). Research published in the British Medical Journal found that “Pregnant women can safely engage in: (1) exercise for up to 35 min at 80%–90% of their maximum heart rate in 25°C and 45% relative humidity; (2) water immersion (≤33.4°C) exercise for up to 45 min;” without reaching a dangerous core temperature. 

These guidelines will suit the exercise needs of most women. The Zwift Baby on Board workouts are structured around these parameters. But there will still be groans of disappointment from athletes who consider 35 minutes of exercise to simply be their warmup, or who recognise that outdoor temperatures are frequently higher than 25°C (77°F). 

Using CORE for peace of mind 

Traditionally, doctors advised pregnant women to exercise for only very short durations at very light intensity. While this recommendation has eased because of extensive research, many women still have lingering unease about exercising while pregnant.  A CORE body temperature monitor can provide peace of mind for pregnant women who are following recommended exercise guidelines.  

While the CORE sensor is not considered a medical device in all countries, it does deliver real-time data that is more relevant than simply relying on heart rate and perceived effort. This can help reassure women that their body temperature is not approaching the danger zone, even though they are staying within the recommended duration and intensity limits. CORE does not recommend exceeding the research-based exercise guidelines, even if core body temperature remains in the safe zone. 

CORE can additionally be used to monitor the body temperature 24/7 by wearing the sensor in “lifestyle mode”. In this way, women can gain useful insights about how baseline temperature changes during pregnancy. 

Elite pregnant athletes training with CORE 

It is not uncommon to read about the elite athletes who continue training at a high level through their pregnancy. The ACOG recommends that pregnant high-level athletes receive frequent and close supervision of their training and that they pay particular attention to avoiding hyperthermia (overheating) and dehydration. Women who want to exceed the recommended exercise guidelines for pregnancy should consult a doctor to determine what is right for them and their babies. 

CORE can then be a useful monitoring tool for high-level training while pregnant. The highly accurate real-time temperature readings give precise data to help women stay within their doctors’ and coaches’ prescribed training advice and avoid elevated core body temperatures that may pose risks. 

Additional resources 

MedicineNet: Is It Safe to Exercise During Pregnancy? 

Runners World: Pregnant Runners: It’s Okay to Keep Training Through the Summer 

Bicycling Australia: Zwift To The Rescue: Pedalling While Pregnant 

Zwift: Baby on Board Workouts