A recap of the history of medical recommendations about exercising during pregnancy.
(*This piece is in reference to healthy, normal pregnancies without contraindications for exercise.)
In a 2016 piece in The Atlantic, writer Julie Beck explained that her “gut reaction” to the prospect of exercise during pregnancy was that it “seems risky.” She is definitely not alone in her intuition – the idea that exercise might be hazardous for pregnant women is pervasive in American society. There appears to be a good deal of confusion about the issue. As of 2014, only about 16% of pregnant women in the U.S. were exercising in accordance with the American College of Obstetricians and Gynecologists (ACOG) guidelines (which suggest engaging in “moderate-intensity exercise for at least 20-30 minutes per day on most or all days of the week”). In 2016, a majority of rural women surveyed for a study published in the International Journal of Childbirth Education conveyed inaccurate or confused understandings about exercising during pregnancy. In a 2010 survey of physicians and certified nurse-midwives in Michigan, a surprisingly high number of practitioners conveyed outdated information to their patients, with 64% of respondents urging pregnant women to “limit their activity intensity based on a suggestion that has not been applicable for several years.” So pregnant women who continue to exercise hear – from medical professionals and from friends and family – that they should “be careful,” or “take it easy.” Women like Julie Beck think instinctively about exercise as “risky.” Where did this kind of apprehension originate? Why are Americans so nervous about the habit of exercising during pregnancy?
American women were taught to be cautious about physical exertion during pregnancy for much of the twentieth century.
Historically, recommendations regarding exercise during pregnancy stemmed from socio-cultural ideas and norms more than they were grounded in science. Generally speaking, pregnant women were “treated as though they had an illness.” They were instructed to “relax, avoid strenuous exertion and even bending or stretching, for fear they would strangle or squash the baby.” In 1949, the U.S. Children’s Bureau exclaimed that pregnant women could maintain housework and gardening activities, could go for walks up to one mile at a time, and could swim from time to time. Most books in the 40s proclaimed something similar, allowing that pregnant women could continue their housework but by and large discouraging sports activities.
Medical textbooks up through the 1960s and even into the 1970s announced that “’pregnancy is not a good time to exercise’” (although they still permitted walking). Meanwhile, scientific medicine was beginning to take “a more serious interest” in exercise as a component of health. Exercise science blossomed in the 1960s, and in the 1970s medical outlets like the National Institutes of Health, the American Heart Association, and the Centers for Disease Control began weighing in. The most rigorous medical journals, such as the Journal of the American Medical Association and The New England Journal of Medicine, started publishing articles on the importance of exercise and physical activity. While exercise grew more popular among the general population, exercising throughout pregnancy was relatively unusual – enough so that JAMA ran a story in 1981 about a woman who ran 4 miles daily throughout her seventh pregnancy. She was the subject of a formal academic presentation at the annual meeting of the American College of Sports Medicine. The fact that this woman’s experience warranted formal comment among medical professionals indicates that practitioners were not accustomed to seeing women continue to exercise while they were pregnant. (By comparison, it is difficult to imagine that professionals today would consider this situation worthy of special discussion.)
Learning What Pregnant Women Already Knew: Pregnant Women Can Be Active
By the end of the 1980s, exercise was not only cemented as a legitimate component of medical health and wellbeing, it was a public fad. Exercise routines for every faction of society – including pregnant women – abounded. Prenatal exercise regimens proliferated so widely, in fact, that doctors grew concerned about them. Most were developed by non-physicians and made untenable claims about how physical fitness would ease labor and delivery. Amid this climate, medicine and society started asking questions about the safety of exercise during pregnancy. According to one analysis, two “schools of thought” emerged: one conservative and the other liberal. Conservatives, predominantly physicians, were more likely to recommend “a restrictive, cautious approach” to pregnant women. In turn, active pregnant women saw no detriments to their activity and argued that exercise was a boon to their pregnancies.
For those who harbored any concerns, there were two broad questions. The first was acute – were there any immediate problems that resulted during exercise for a mother or a fetus? The second was chronic – were there any broad negative outcomes of exercising on the course of a pregnancy and/or birth?
Some of the first work conducted took place on animals, and those studies seemed to point to some potential risks, such as reduced maternal blood flow (which could be problematic if it caused a reduction in adequate blood supply to the uterus) and lower birth weight. But human research indicated otherwise. Small-scale studies in the 1980s concluded that exercise did not impact fetal weight and that any effects on maternal blood flow or fetal heart rate were limited to exercise sessions, were minor, and had no visible consequences. So, in the short-term, exercise did elicit subtle acute changes, but they were not evidently harmful. And in the long-term, exercise appeared to offer benefits.
Then people starting asking more specifics – how hard could women work out? For how long? In what kind of exercises and activities could they partake? As researchers dug into these questions, they increasingly determined that vigorous or strenuous exercise posed no problems, and might in fact be advantageous. One 1987 study, for example, looked at nearly 850 women split into four groups – a control group, a low-exercise group, a medium-exercise group, and a high-exercise group. Across all three exercising groups, physical activity did not have any negative outcomes for mothers or babies. C-section rates were actually inversely correlated with higher exercise intensity, and the high-exercisers gave birth to babies with the highest Apgar scores. “Pregnancy outcomes,” the researchers concluded, “were more favorable in the exercise groups, particularly the high-exercise group.” With some (albeit minimal) research, ACOG levied a formal opinion.
In 1985, ACOG released its first ever guidelines on exercising during pregnancy, formally approving of exercise in pregnant women. Given the paucity of research, its recommendations were relatively cautious. Pregnant women were advised to limit their maximum heart rates to 140 beats per minute, restrict strenuous activity to no more than 15 minutes, and keep their core body temperatures below 100.4 degrees Fahrenheit. In 1994, ACOG amended its guidelines, doing away with heart rate restrictions and time limitations. In 2002, another revision asserted that “pregnant women are now encouraged to follow general adult recommendations for PA [physical activity].”
At the end of 2015 ACOG released its current guidelines, which stress that exercising during pregnancy carries very little risk. They suggest that all pregnant women without complications should partake in aerobic and strength training exercises for the duration of their pregnancies. This advisement is similar internationally. Breaking with its previous guidelines, ACOG also began to encourage women to start exercising during pregnancy, even if they hadn’t previously. Women who were exercising pretty vigorously before they became pregnant also gained the A-OK to “keep doing the same workouts” if they felt up for it. (One piece of the original guidelines that research has continually substantiated is the advisement that pregnant women keep their core body temperatures under about 102 degrees Fahrenheit, since elevated core body temperatures (especially in the first trimester) have been correlated with neural tube defects.)
Allowing that the pregnant body often demands numerous modifications for exercising women, ACOG’s general message is that exercise prescriptions for pregnant women should essentially be “the same…as those recommended for the general population.” With regards to exercise, pregnant ladies can work out just like everybody else. (If they want to.)
The Scope of Things
In other words, science clearly demonstrated that the age old customs and “social wisdom” supposing that pregnant women should avoid physical activity were misguided. At the present, evidence clearly shows that exercising during pregnancy carries no increased risks for the fetus or for the mother. It also has no documented associations with miscarriage or premature labor. In some ways, the benefits of exercising during pregnancy are modest. As Emily Oster assesses in her wonderful book Expecting Better, many studies suggest that “exercise doesn’t seem to have much of an impact on anything…[and] the same randomized studies that show no clear benefits of exercise also show no downsides.” But more and more work seems to indicate that exercising during pregnancy does in fact carry potential benefits, and that on the whole, it is likely beneficial for both mothers and babies.
Exercise offers many of the same overall benefits for pregnant women as it does for the general population – improving physical fitness, helping with weight management, and improving mood. (Regarding weight, exercising while pregnant only helps a little – just as outside of pregnancy. A 2014 metaanlysis showed that exercising while pregnant lowered prenatal weight gain by about 2.2 pounds on average.) It also has some possible benefits particular to pregnant women, ranging from decreasing the risk of gestational diabetes and hypertension to helping with typical maladies such as back pain, constipation, bladder control, varicose veins, and heartburn. Some women report that a quick bout of exercise (just 3-5 minutes) relieves morning sickness symptoms. New York Times contributor Gretchen Reynolds recently wrote about a fascinating study in which the offspring of mice who ran while they were pregnant ran more themselves when they grew up – they “had literally been born to run,” she quipped. The study, as Reynolds describes, “hint[s] at the possibility that to some extent our will to work out may be influenced by a mother’s exercise habits during pregnancy, and begin as early as in the womb.”
Even more provocatively, recent research shows that being physically active during her pregnancy might reduce a woman’s chances of having a C-section. In a systematic review of randomly-controlled trials (published in 2014 in the American Journal of Obstetrics and Gynecology) encompassing more than 3300 women in 16 studies, authors measured that “women in exercise groups had a significantly lower risk of cesarean delivery.” Importantly, only one of the studies included in the review actually offered any indication about the circumstances of C-sections, meaning they did not record or explain why C-sections occurred. This is definitely a huge factor, since many women elect to have C-sections ahead of time. Still, the numbers are hard to ignore – really hard to ignore, actually. Exercise programs had the potential to lower the risk of C-section by about 15%. As the authors note, this possibility “is of huge clinical significance…and likely [is] difficult to obtain by any other single intervention.”
Popular websites and common resources for pregnant women working to transmit these findings to women mostly do a nice job. Sometimes they send mixed messages, or patronize women by belittling the manifold obstacles to exercise that pregnancy imposes. But they are working against decades of cultural and ideological conventions relegating pregnant women to inactivity or domestic work. There are, of course, exercise modifications women should make as well as some activities pregnant women really should avoid altogether (such as scuba diving, or contact sports), but the ongoing scholarship should reassure women who wish to remain active during their pregnancies. The recommendations I heard when I was pregnant were to simply do what felt comfortable, safe, and good, based on my own intuition. Of course, this was welcome advice, but I liked knowing more of the full story.
 Julie Beck, “Exercise, for a Healthier Pregnancy,” The Atlantic, July 8, 2016, http://www.theatlantic.com/health/archive/2016/07/exercise-for-a-healthier-pregnancy/490424/.
 The American College of Obstetricians and Gynecologists, “Committee Opinion: Physical Activity and Exercise During Pregnancy and the Postpartum Period” Committee Opinion 650 (December 2015): 401.e10; ibid., 1.
 Dana M. Dillard, “Exercise and Pregnancy,” International Journal of Childbirth Education 31, no. 1 (January 2016): 9.
 Patricia W. Bauer, Clifford L. Broman, and James M. Pivarnik, “Exercise and Pregnancy Knowledge Among Healthcare Providers,” Journal of Women’s Health 19, no. 2 (2010): 337.
 George F. Winter, “Evidence on Exercise in Pregnancy,” British Journal of Midwifery 23, no. 12 (December 2015): 844; Danielle Symons Downs et al., “Physical Activity and Pregnancy: Past and Present Evidence and Future Recommendations,” Research Quarterly for Exercise and Sport 83, no. 4 (December 2012): 2; Bauer, Broman, and Pivarnik, “Exercise and Pregnancy Knowledge Among Healthcare Providers,” 335; Raul Artal and Susan Kelemen Gardin, “Historical Perspectives,” in Exercise in Pregnancy, ed. Raul Artal, Robert A. Wiswell, and Barbara L. Drinkwater, II (Baltimore, Maryland: Williams & Wilkins, 1991), 1.
 Roni Caryn Rabin, “Ask Well: Is It Safe to Exercise During Pregnancy?,” New York Times, March 20, 2016, http://well.blogs.nytimes.com/2016/03/10/ask-well-pregnancy-and-exercise/?_r=0; Pamela Shrock, “Exercise and Physical Activity During Pregnancy,” in Global Library of Women’s Medicine, 2008, https://www.glowm.com/section_view/heading/Exercise%20and%20Physical%20Activity%20During%20Pregnancy/item/98; Roger L. Hammer, Jan Perkins, and Richard Parr, “Exercise During the Childbearing Year,” The Journal of Perinatal Education 9, no. 1 (2000): 5.
 Downs et al., “Physical Activity and Pregnancy: Past and Present Evidence and Future Recommendations,” 3.
 Artal and Gardin, “Historical Perspectives,” 4.
 Roni Caryn Rabin, “Ask Well: Is It Safe to Exercise During Pregnancy?,” New York Times, March 20, 2016, http://well.blogs.nytimes.com/2016/03/10/ask-well-pregnancy-and-exercise/?_r=0.
 Milan Korcok, “Pregnant Jogger: What a Record!,” JAMA 246, no. 3 (July 1981): 201.
 Jack W. Berryman, “Exercise Is Medicine: A Historical Perspective,” Current Sports Medicine Reports 9, no. 4 (2010): 3–5; Pamela Shrock, “Exercise and Physical Activity During Pregnancy,” in Global Library of Women’s Medicine, 2008, https://www.glowm.com/section_view/heading/Exercise%20and%20Physical%20Activity%20During%20Pregnancy/item/98.
 Artal and Gardin, “Historical Perspectives,” 5.
 Roger L. Hammer, Jan Perkins, and Richard Parr, “Exercise During the Childbearing Year,” The Journal of Perinatal Education 9, no. 1 (2000): 2.
 Catherine A. Collings, Luis B. Curet, and John P. Mullin, “Maternal and Fetal Responses to a Maternal Aerobic Exercise Program,” American Journal of Obstetrics and Gynecology 145, no. 6 (March 1983): 702; John C. Jarrett and William N. Spellacy, “Jogging During Pregnancy: An Improved Outcome?,” Obstetrics and Gynecology 61, no. 6 (1983): 706, 708.
 Collings, Curet, and Mullin, “Maternal and Fetal Responses to a Maternal Aerobic Exercise Program,” 705, 706; Jarrett and Spellacy, “Jogging During Pregnancy: An Improved Outcome?,” 708; Lawrence D. Platt et al., “Exercise in Pregnancy: II. Fetal Responses,” American Journal of Obstetrics and Gynecology 147, no. 5 (November 1983): 487–91; Jean-Claude Veille et al., “The Effect of Exercise on Uterine Activity in the Last Eight Weeks of Pregnancy,” American Journal of Obstetrics and Gynecology 151, no. 6 (March 1985): 727, 730.
 Douglas C. Hall and David A. Kaufmann, “Effects of Aerobic and Strength Conditioning on Pregnancy Outcomes,” American Journal of Obstetrics and Gynecology 157, no. 5 (1987): 1199, 1201–2.
 Danielle Symons Downs et al., “Physical Activity and Pregnancy: Past and Present Evidence and Future Recommendations,” Research Quarterly for Exercise and Sport 83, no. 4 (December 2012): 3; Patricia W. Bauer, Clifford L. Broman, and James M. Pivarnik, “Exercise and Pregnancy Knowledge Among Healthcare Providers,” Journal of Women’s Health 19, no. 2 (2010): 335.
 Bauer, Broman, and Pivarnik, “Exercise and Pregnancy Knowledge Among Healthcare Providers,” 335–36.
 Raul Artal, “Exercise in Pregnancy: Guidelines,” Clinical Obstetrics and Gynecology 59, no. 3 (September 2016): 639–40.
 American College of Obstetricians and Gynecologists, “Exercise During Pregnancy: FAQ,” May 2016, http://www.acog.org/Patients/FAQs/Exercise-During-Pregnancy.
 Hammer, Perkins, and Parr, “Exercise During the Childbearing Year,” 6; Robert W. Jarski and Diane L. Trippet, “The Risks and Benefits of Exercise During Pregnancy,” Journal of Family Practice 30, no. 2 (February 1990): 185.
 Artal, “Exercise in Pregnancy: Guidelines,” 640.
 George F. Winter, “Evidence on Exercise in Pregnancy,” British Journal of Midwifery 23, no. 12 (December 2015): 844; Emma Lewis, “Exercise in Pregnancy,” Australian Family Physician 43, no. 8 (August 2014): 541.
 Adrienne Parad, Elizabeth Leonard, and Lara Handler, “Exercise and Pregnancy Loss,” American Family Physician 91, no. 7 (2015): 437; Hammer, Perkins, and Parr, “Exercise During the Childbearing Year,” 5.
 Emily Oster, Expecting Better: Why Conventional Pregnancy Wisdom Is Wrong--and What You Really Need to Know (New York: Penguin Books, 2013), 154.
 Iris Domenjoz, Bengt Kayser, and Michel Boulvain, “Effect of Physical Activity During Pregnancy on Mode of Delivery,” American Journal of Obstetrics and Gynecology 211 (October 2014): 401.e10.
 American College of Obstetricians and Gynecologists, “Exercise During Pregnancy: FAQ”; Bauer, Broman, and Pivarnik, “Exercise and Pregnancy Knowledge Among Healthcare Providers,” 335; Hammer, Perkins, and Parr, “Exercise During the Childbearing Year,” 4.
 Gretchen Reynolds, “Does Exercise During Pregnancy Lead to Exercise-Loving Offspring?,” New York Times, April 6, 2016, http://well.blogs.nytimes.com/2016/04/06/are-we-born-to-run/.
 Domenjoz, Kayser, and Boulvain, “Effect of Physical Activity During Pregnancy on Mode of Delivery,” 401.e1.
 see also ibid., 401.e8, 401.e10; Ruben Barakat et al., “Exercise During Pregnancy Reduces the Rate of Cesarean and Instrumental Deliveries: Results of a Randomized Controlled Trial,” The Journal of Maternal-Fetal and Neonatal Medicine 25, no. 11 (2012): 2372–76.