Traditionally, many healthcare practitioners were concerned that maternal exercise and its increased physiological demand might have adverse effects for the unborn child. Not only do we now know that this is not the case, there are many benefits for the baby that come from the mother’s exercise regimen.
The Baby’s Physical Responses to Maternal Exercise
The safe stress placed on the baby during regular maternal exercise helps to improve the baby’s ability to cope with the reductions in uterine blood flow and oxygen delivery that happen daily. Furthermore, this provides additional protection when an unanticipated maternal stress occurs such as during serious traumatic injury, other medical emergencies, and if complications arise during labor.
The fetal heart rate is changed from maternal exercise, but its change is related to the components of exercise and characteristics of the woman. The fetal heart rate went up during and immediately after exercise, but gradually returned to its pre-exercise baseline once the session ended. It was found that the duration of exercise was important as it had to be continued for at least 10 minutes to see a consistent change in the fetal heart rate response. In addition, the longer the woman exercised over the 10 minute threshold, the greater the increase in the fetal heart rate. The type of exercise was important as well. Weight-bearing exercise resulted in a greater increase in fetal heart rate than non-weight-bearing exercise. Also, the intensity of the exercise was a factor.
When you combine the duration of exercise with the type of exercise and intensity of the exercise as above, it seems that the increase in fetal heart rate was most likely due to a fall in uterine blood flow during that time. Weight-bearing exercise requires the woman to use a larger fraction of her muscle mass to move her weight against gravity. This intensifies the need for blood flow distribution away from the internal organs to supply the increased need for the muscle mass. When the uterine blood flow decreases, the oxygen delivery is also decreased, which causes the baby’s heart rate to increase.
But the big question is, what is the safe upper limit of the increase in fetal heart rate. There must be a value to the decrease in uterine blood flow to where the resultant increase in fetal heart rate is not safe. Through the observation of fetal breathing, activity, and bowel function, it was determined that an increase in fetal heart rate as high as 25 to 35 beats per minute is OK. Likewise, if a baby’s heart rate goes up over 180 beats per minute, this is deemed unsafe. If this occurs, the woman should lie down on her left side so as to not compromise the blood flow in the body.
Baby’s Condition During Labor
At the beginning of labor, only 1-2 percent of babies being carried by exercising mothers worried doctors compared to 5 percent in non-exercising mothers and 10 percent in mothers who exercised, then stopped in late pregnancy.
During labor, the babies being born to mothers who continued to exercise tolerated the stress of contractions much better than the non-exercising mothers and the mothers who stopped exercising in late pregnancy. Their incidence of a doctor, nurse, or midwife becoming concerned about the baby’s condition was less than half of the other groups.
The observation of fetal bowel movement, blood sampling, and fetal heart rate showed that babies of exercising mothers were tougher. The stresses of late pregnancy and labor didn’t produce as many warning signs of difficulty requiring attention during labor when compared to the non-exercising mothers or those who stopped exercising in late pregnancy.
We have talked before about how the babies of exercising moms are lighter and leaner without any signs of growth retardation. But we haven’t talked about how these babies were reportedly easier to care for. Data shows that these babies slept through the night earlier on than those from non-exercising mothers and those stopping in late pregnancy. Also, these babies had less incidence of colic. Furthermore, they are being show to respond more readily to things in their environment and are able to self-quiet when they are disturbed much better than the other babies. Both of these may suggest that babies from exercising mothers are more mature at birth.
Moral of the story, exercise is not only safe for the mother and the baby, it produces many important benefits and is highly recommended. Remember, these findings were based on the mother engaging in regular, weight-bearing exercise 3 days per week, for at least 20 minutes per session, at a moderate to moderately high intensity level. KEEP EXERCISING THROUGHOUT THE ENTIRE PREGNANCY. DON’T STOP AT THE END.
Remember, pain-free first, then performance.
Knowing the facts is more important than listening to the opinions.
Always live life stronger.
*Michael Satterley is a doctor of physical therapy and the Director of Sports Therapy Programs at Tidewater’s Performance Center / Oyster Point Physical Therapy Clinic in Newport News.