Lifting weights during pregnancy
You’ve probably seen the pictures on social media and in the news: a very pregnant woman, with a heavy barbell on her shoulders, mid squat, in an Olympic powerlifting move. But is it safe to lift heavy weights for exercise during pregnancy?
Exercise during pregnancy is not only healthy for mom, but also for baby. The U.S. Department of Health and Human Services recommends that pregnant women get at least 150 minutes of moderate-intensity aerobic activity per week. The American College of Obstetrics and Gynecology also recommends that:
- A pregnant woman should be evaluated by her doctor to rule out possible reasons not to exercise.
- If doctor-approved for exercise, a pregnant woman should engage in regular, moderate-intensity physical activity to continue getting the same associated health benefits during pregnancy as she did before pregnancy.
While these are good foundations for exercise during pregnancy, there are still important questions that have yet to be answered, such as: What about different types of exercise such as weightlifting and interval training? What exactly are “moderate” and “vigorous” exercise for pregnant women? Recently, the issue of lifting heavy objects while pregnant has gained some attention in the media and fitness communities. When it comes to heavy lifting, the research verdict is still out. The guidelines for lifting and pregnancy are often taken from occupational studies, where women have to lift objects as part of their jobs, not necessarily to improve their fitness. In addition, organized studies on pregnant women are ethically complicated, so determining the effects of certain types of exercise can be difficult.
What We Know
There are some things about exercise and pregnancy that we know for certain. First, pregnant women should avoid being supine (on their backs) for extended periods of time. For example, sit-ups or supine bench presses are not safe and should be avoided because of the risk of cutting off blood flow to the fetus. Also, any activity that increases the risk of falling, specifically on the belly, should also be limited. Examples include skiing, box jumps, and contact sports.
There is research both to support and refute the safety of heavy lifting on fetal health. Some studies that have found that lifting heavy weight increases the risk of pre-term birth. These risks seem to affect women who are less than 12 weeks pregnant and lift heavy loads multiple times per day. However, other studies suggest that lifting heavy weights in the later stages of pregnancy does not seem to have negative effects on the baby, at least in those women who have experience with weight training prior to being pregnant.
It’s also important to remember that the physical changes that come with pregnancy can affect both the ability to do exercises and how various forms of exercise affect a woman’s body. For example, pregnancy changes a women’s overall body mass and center of mass, as well as spinal curvature, which may cause spinal instability, along with changes in balance and increase in flexibility around joints. These factors and others may affect the way a pregnant woman performs exercises, even ones she may have engaged in prior to pregnancy.
Most of the data about lifting during pregnancy come from studies of occupational lifting. But these conditions are very different from those of a gym for fitness center where the aim of lifting weights is to improve muscular fitness. As a result, it’s difficult to conclude that fitness-related heavy weightlifting will have the same effects as work-related heavy weightlifting. And that also means that the specific concerns and recommendations for occupational lifting may not translate for recreational lifting.
Debrief (Military Relevance)
Exercise during pregnancy is healthy for both mother and baby. More often than not, women don’t get enough exercise during this time; but for highly fit, even elite, athletes, the research is limited on “how much is too much” when it comes to exercise during pregnancy. More research is needed in the specific area of heavy weightlifting for fitness during pregnancy, not just for job-related activities. This is especially important for women in the military, whose job demands lead them to participate in weightlifting exercise to keep up their fitness.
Each service has its own guidelines and polices regarding exercise and care for pregnant service members. Pregnant women should avoid the high-risk exercises and postures discussed above. Women who have a history of pre-term labor, cervical incompetency, and other conditions their doctors identify as high risk should work closely with their healthcare professional in terms of what exercises are appropriate. Be sure to consult your doctor about the kinds of exercises that are right for you and your baby before you begin any exercise program. And for a more in-depth look at the research behind the issues, read HPRC’s Research Brief, “Weightlifting During Pregnancy.”
- Exercise and physical activity are important during pregnancy, for the health of the mother and the baby. However, the guidelines are unclear on intensities and types of exercises that are safe.
- Guidelines for lifting during pregnancy are often derived from occupational studies and may not be applicable to lifting for exercise.
- Pregnant women need to consult with their doctor before beginning an exercise program, or about the safety and limitations to their current exercise program.
The benefits of exercise during pregnancy are well established. The American College of Obstetrics and Gynecology recommends that each woman be evaluated individually, and in the absence of contraindications, “pregnant women should be encouraged to engage in regular, moderate intensity physical activity to continue to derive the same associated health benefits during their pregnancies as they did prior to pregnancy.”1 In addition, the U.S. Department of Health and Human Services recommends that pregnant women attain at least 150 minutes of moderate-intensity aerobic activity per week. However, according to national trends in self-reported physical activity, less than 25% of pregnant women meet the recommendations for moderate to vigorous physical activity. These guidelines are a good foundation for encouraging physical activity during pregnancy but also leave open the question of the relative risks and benefits of different exercise modalities (such as weight lifting) and what constitutes “moderate intensity.” These current exercise guidelines also do not address or define “vigorous” or “strenuous” exercise behaviors. While most women appear to fall short of meeting these standards, there are women at the other end of the spectrum, such as highly fit and elite athletes who exceed the minimum recommendations on a regular basis (pregnant or not). There is limited research on this subgroup of women in regards to the safety of these exercises. Where studies have been performed, typically the testing modality has been running, and fetal outcomes such as early pregnancy loss, low birth weight, and preterm delivery were not assessed in a follow up test. Recently, the question of the safety and benefits of heavy weightlifting, such as power lifting and Olympic lifting, among pregnant athletes has come back into focus.
Facts and Evidence
Many of the concerns related to exercise during pregnancy come from data that look at prolonged standing and repetitive strenuous physical work associated with fetuses who are small for their gestational age.2 However, more recent studies (see below) have shown that fetal growth and outcomes are influenced by many other factors, which may include heavy and/or repetitive lifting.
There is some evidence that lifting heavy weights can affect fetal outcomes and increase the risk of pre-term birth. The risk seems higher in women less than 12 weeks pregnant whose occupations require them to lift heavy loads multiple times per day and multiple loads that add up to more than 1000kg a day.3-5
By contrast, lifting heavy weights in the later stages of pregnancy does not seem have negative effects on the fetus, at least among patients who have experience with weight training for exercise—described as the “healthy lifter” effect.5
The act of trunk bending more than one hour per day was found to increase the risk for pre-term delivery nearly threefold.6 The effects of forward trunk bending have not been studied. Researchers speculate that increased intra-abdominal pressure may be the associated risk factor, especially during the third trimester when space in the abdominal cavity is greatly reduced.
A few small/limited studies have looked specifically at weight training among pregnant women, although primarily based on “light” or self-reported prior exercise habits.7-9 They found no apparent effects on risk of pre-term labor, mode of delivery, or gestational age at delivery. They also suggested that resistance exercise by pregnant women seems to reduce hypertensive disorders and gestational diabetes. In short, light resistance exercise performed regularly during the second and third trimester does not seem to affect birth weight or other fetal outcomes, and even moderate- to high-intensity exercise by well-conditioned women does not appear to have adverse effects.
It is also important to consider biomechanical changes that occur with pregnancy which have the potential to affect exercise performance. Anthropometric changes that occur include increase in overall body mass, particularly in the upper body, changes in the center of mass (COM), increased abdominal girth, and changes in spinal curvature. There may also be changes in balance control, joint laxity, and potential spinal instability. The latter may influence one’s ability to lift heavy weights appropriately and with proper form.
The conditions of occupational lifting are different than those of focused weightlifting in a controlled setting, such as a gym or fitness center. Occupational lifting isn’t usually performed with the focus of improving muscular fitness, so it is difficult to use the occupational data for conclusive evidence in regards to athletic weight training. With occupational lifting, the weight is often not lifted in a straight-line movement, in “sets,” with focused control, or within a concentrated period of time. There are certain postures that pregnant women should avoid during exercise. After the first trimester, women should avoid any exercise that involves lying supine (e.g., sit ups, supine bench presses) or standing motionless for any length of time, which decrease venous return. Activities that increase the risk for falling, which can be exacerbated by the anthropometric (see above) and biomechanical changes noted above, should also be avoided.1
Women who have a history of pre-term labor, cervical incompetency, and other absolute contraindications to exercise during pregnancy should also consult their healthcare professional with regard to what exercises are appropriate.1
Each branch has its own guidelines and policies regarding exercise for pregnant servicewomen. They are placed on profile and exempt from regular mandatory physical fitness training, and may be enrolled in special pregnancy fitness program (available in the Army) or encouraged to maintain their own exercise program. With little to no supervision of their personal exercise programs, many service women may not be aware of the types of exercise they should or should not perform.1 Also, as women are integrated into new combat roles, there may be increased pressure to maintain and return to peak fitness during and after pregnancy. The safety of mother and baby are paramount when deciding on an appropriate fitness regimen on an individual basis.
By in large, the safety of an exercise program, including weight lifting, during pregnancy is mostly determined by the types of exercises and by the health and fitness level of the mother and with consultation and clearance from her physician. While there is evidence for and against heavy lifting while pregnant, most of the studies are with regard to heavy lifting as part of an occupation, which may not translate to the kind of heavy lifting involved in exercise. The lack of scientific study is likely due to the risks (to both fetus and mother) associated with studying exercise in pregnant women. More research is also needed in the specific area of exercise and activities that include bending at the waist and associated natal outcomes.
- Committee on Obstetric P. ACOG committee opinion. Exercise during pregnancy and the postpartum period. Number 267, January 2002. American College of Obstetricians and Gynecologists. International journal of gynaecology and obstetrics: the official organ of the International Federation of Gynaecology and Obstetrics. 2002;77(1):79-81.
- Launer LJ, Villar J, Kestler E, de Onis M. The effect of maternal work on fetal growth and duration of pregnancy: a prospective study. British journal of obstetrics and gynaecology. 1990;97(1):62-70.
- Ahlborg G, Jr., Bodin L, Hogstedt C. Heavy lifting during pregnancy--a hazard to the fetus? A prospective study. International journal of epidemiology. 1990;19(1):90-7.
- Juhl M, Strandberg-Larsen K, Larsen PS, Andersen PK, et al. Occupational lifting during pregnancy and risk of fetal death in a large national cohort study. Scandinavian journal of work, environment & health. 2013;39(4):335-42.
- Runge SB, Pedersen JK, Svendsen SW, Juhl M, et al. Occupational lifting of heavy loads and preterm birth: a study within the Danish National Birth Cohort. Occupational and environmental medicine. 2013;70(11):782-8.
- Bonzini M, Coggon D, Godfrey K, Inskip H, et al. Occupational physical activities, working hours and outcome of pregnancy: findings from the Southampton Women's Survey. Occupational and environmental medicine. 2009;66(10):685-90.
- Barakat R, Lucia A, Ruiz JR. Resistance exercise training during pregnancy and newborn's birth size: a randomised controlled trial. International journal of obesity. 2009;33(9):1048-57.
- Kardel KR, Kase T. Training in pregnant women: effects on fetal development and birth. American journal of obstetrics and gynecology. 1998;178(2):280-6.
- White E, Pivarnik J, Pfeiffer K. Resistance Training During Pregnancy and Pregnancy and Birth Outcomes. Journal of physical activity & health. 2013.