There are obvious reasons to exercise during pregnancy: fewer aches and pains for mom, less weight gain, more energy, the list goes on. The stories of women working out until the day they went into labor are numerous. I did it with my two girls.
While anecdotal evidence is great, here we go into the science behind why exercise is so beneficial and recap findings by Dr. James F. Clapp III, an OB/GYN who followed more than 250 marathon runners through their pregnancies.
1. A crazy amazing placenta
Okay, all placentas do amazing things. Essentially the lifeline between a mom and baby, the placenta is an organ that provides oxygen and nutrients to baby while providing mom with the hormones, thermo-regulation, and infection-fighting power to ensure a healthy pregnancy.
But Dr. James F. Clapp, OB/GYN, and author of “Exercising Through Your Pregnancy,” concluded that the placentas of women who workout early in their pregnancies grow faster and function better, transferring more oxygen and nutrients to the baby. According to Clapp, these benefits last throughout pregnancy, even if the woman stops exercising. This is true even of women who start exercising after becoming pregnant.
Clapp admits that this benefit probably doesn’t make a huge difference as placentas of exercising women and non-exercising women do an adequate job of supporting and protecting baby. But, if a problem such as a hemorrhage were to occur, Clapp writes, “the exercising woman’s placenta can do a better job of maintaining fetal nutrition and oxygenation.”
2. The cardiovascular system of a Greek goddess
When a woman becomes pregnant, the blood her heart pumps continues to support all of her systems, but is also redirected to support the growing baby. It takes a few weeks for the heart to adapt and pump more blood to fully support the woman and baby. During this time, many women report feeling dizzy or lightheaded when standing.
Once the body adapts by the twelfth week, the increase in heart and blood volume in pregnant women is akin to blood doping. This is exacerbated in women who exercise. According to Clapp, plasma volumes, red cell volumes, total blood volumes, in fit pregnant women are 10 to 15 percent higher and the amount of blood pumped by the heart is 30 to 50 percent greater.
After the 1976 Olympics, rumors surfaced that young athletes from East Germany were forced to have sex with their coaches in an effort to get them pregnant and those pregnancies were ended after the first trimester, in time for the Games. Although never proven, the term “abortion doping” was coined.
3. That cardiovascular system keeps performing after birth
Women who workout during their pregnancies maximize the benefits of their cardiovascular systems. In addition to increased blood and plasma, lung adaptations, alveolar ventilation and gas transfer at tissue level improve. The combination of training and pregnancy improves maximal aerobic capacity 5 to 10 percent. This becomes apparent six months to 1 year after giving birth.
Although no studies have investigated whether muscle mass or muscle function changes during pregnancy, Clapp observed that both mass and strength increased in the women he followed — possibly because they were essentially carrying around 20-pound kettlebell for several months.
4. Earlier, shorter deliveries
Clapp’s research found that women who exercised delivered, on average, 5-7 days earlier than those that did not exercise. He also found that women who exercised vigorously had a 50 percent chance of delivering before her due date (but still full term), a distinct plus if you happen to be the pregnant woman.
Regular exercise also shortened labor by about a third. A third.
**On a personal note: this last finding did not prove true for me. I was in early labor with both of my girls for 10-12 hours; but once I could push, I got them out in under 10 minutes.**
Not surprisingly, Clapp found that those who continued exercising throughout pregnancy had a marked decrease in the need for all types of medical intervention including:
5. Smaller (but still very healthy!) babies
Clapp found that the pregnant women who exercised delivered smaller, but still very healthy, babies. The average weight of babies born to women who exercised: 7.2 ounces. This is 14 ounces lighter than babies born to women who did not exercise. Babies born to women who exercised also had less body fat, 11 percent as opposed to 16 percent. Length and head growth remained comparable.
Clapp also found that, though smaller, “babies born to women who exercised had no trouble regulating their temperature or blood sugar and did not struggle with early weight loss.”
Catherine Cram, fitness consultant and co-author of “Exercising Through Your Pregnancy,” said lower birth weight doesn’t mean trouble and heavier babies does not necessarily mean they are healthier.
“Leaner babies may have a better chance of not developing obesity later in life since they’re born with less fat cells,” she says. “The bigger the baby the greater the risks of complications during birth.”
Cram said “lean” babies still fall within what is considered a normal birth weight, between 5.8-9 pounds.
“The sweet spot is around 7 pounds,” she says. “and that’s what we normally see with babies of exercising mothers.”
Disclaimer: Andrea Signor is a writer. She does not have any medical background or fitness certifications. She is a former journalist with an interest in weightlifting. Any woman interested in exercising and lifting in her pregnancy should consult with her medical team and fitness coaches.