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Exercise in pregnancy!

Published:February 21, 2017DOI:https://doi.org/10.1016/j.ajog.2017.01.023
      Related article, page 340.
      In this issue of the American Journal of Obstetrics and Gynecology, Wang et al
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      report results from a randomized controlled trial (RCT) on exercise in pregnancy. They found that cycling exercises initiated at <13 weeks gestation that are performed no <30 minutes 3 times per week until 37 weeks gestation significantly reduced the incidence of gestational diabetes mellitus (GDM) and gestational weight gain at <25 weeks gestation and lowered birthweight in a study that included 300 overweight or obese women carrying singleton gestations. Although these investigators found no significant differences between the exercise and control groups in the incidence of other outcomes such as preterm birth (PTB), gestational hypertension (GHTN), cesarean delivery, and macrosomia, all these outcomes were less frequent in the exercise group.
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      This RCT is in agreement with previous data.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      • Kramer M.S.
      • McDonald S.W.
      Aerobic exercise for women during pregnancy.
      • Han S.
      • Middleton P.
      • Crowther C.A.
      Exercise for pregnant women for preventing gestational diabetes mellitus.
      • Ceysens G.
      • Rouiller D.
      • Boulvain M.
      Exercise for diabetic pregnant women.
      • Meher S.
      • Duley L.
      Exercise or other physical activity for preventing pre-eclampsia and its complications.
      There are indeed >50 RCTs published on exercise in pregnancy. These have been summarized in several metaanalyses.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      • Kramer M.S.
      • McDonald S.W.
      Aerobic exercise for women during pregnancy.
      • Han S.
      • Middleton P.
      • Crowther C.A.
      Exercise for pregnant women for preventing gestational diabetes mellitus.
      • Ceysens G.
      • Rouiller D.
      • Boulvain M.
      Exercise for diabetic pregnant women.
      • Meher S.
      • Duley L.
      Exercise or other physical activity for preventing pre-eclampsia and its complications.
      Often dietary counseling or other dietary interventions, which are beneficial by themselves, have been studied together with exercise,
      • Muktabhant B.
      • Lawrie T.A.
      • Lumbiganon P.
      • Laopaiboon M.
      Diet or exercise, or both, for preventing excessive weight gain in pregnancy.
      • Bain E.
      • Crane M.
      • Tieu J.
      • Han S.
      • Crowther C.A.
      • Middleton P.
      Diet and exercise interventions for preventing gestational diabetes mellitus.
      so it is important, as done by Wang et al,
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      to focus on just exercise data when reviewing the previous literature. Two recent metaanalyses focused on just the effects of exercise on pregnancy outcomes.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      A metaanalysis of 9 RCTs that included 2059 women with an uncomplicated, singleton pregnancy with normal body mass index showed that women who were assigned randomly to aerobic exercise had similar incidence of PTB, 49% lower incidences of GDM, 79% lower incidence of GHTN disorders, 18% lower incidence of cesarean delivery, and a 9% higher rate of vaginal delivery.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      A recent metaanalysis that focused, as in Wang et al,
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      on overweight or obese women included 9 RCTs and 1502 women and showed benefits of exercise in terms of a 38% lower rate of PTB and 39% lower rate of GDM (Table 1).
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      Table 1Benefits of exercise in pregnancy
      Lower incidence of:Higher incidence of:
      Excessive gestational weight gain
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      • Muktabhant B.
      • Lawrie T.A.
      • Lumbiganon P.
      • Laopaiboon M.
      Diet or exercise, or both, for preventing excessive weight gain in pregnancy.
      Vaginal delivery
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      Gestational diabetes mellitus
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      Gestational hypertensive disorders
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      Defined as gestational hypertension or preeclampsia
      Preterm birth
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      Cesarean delivery
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      Birthweight
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      Lower birthweight.
      Berghella. Exercise in pregnancy! Am J Obstet Gynecol 2017.
      a Defined as gestational hypertension or preeclampsia
      b Lower birthweight.
      Our main aim in this editorial is to summarize this now extensive body of level-1 data, based on RCTs and metaanalyses of RCTs, so to provide easy-to-use advice for pregnant women and for us, their providers.
      First, what are the benefits and harm of exercise in pregnancy? Table 1 lists the many statistically significant benefits of exercise in pregnancy that were reported in RCTs and metaanalyses of RCTs.
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      • Muktabhant B.
      • Lawrie T.A.
      • Lumbiganon P.
      • Laopaiboon M.
      Diet or exercise, or both, for preventing excessive weight gain in pregnancy.
      The list is quite noteworthy. To our knowledge, there is no intervention that we as providers can recommend to pregnant women as impressive in its significant impact on so many maternal and perinatal outcomes. Although nonpregnant data would perhaps predict that exercise decreases the incidence of GDM, the fact that exercise significantly decreases GHTN disorders, PTB, and cesarean delivery is remarkable and destroys the myth that exercise might be harmful in pregnancy, especially in terms of PTB. Moreover, there are good reasons why exercise would be associated with these many benefits. Exercise may decrease the incidence of GDM by attenuating the increase in insulin resistance that is associated with pregnancy.
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      It may decrease the risk of GHTN disorders by reducing oxidative stress and therefore improving endothelial function.
      • Genest D.S.
      • Falcao S.
      • Gutkowska J.
      • Lavoie J.L.
      Impact of exercise training on preeclampsia: potential preventive mechanisms.
      Exercise may decrease the incidence of cesarean delivery (and importantly increase the incidence of vaginal delivery) by improving maternal physical fitness and lowering birthweight.
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      We could not identify any harm reported in level-1 data on exercise in pregnancy.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      • Kramer M.S.
      • McDonald S.W.
      Aerobic exercise for women during pregnancy.
      • Han S.
      • Middleton P.
      • Crowther C.A.
      Exercise for pregnant women for preventing gestational diabetes mellitus.
      • Ceysens G.
      • Rouiller D.
      • Boulvain M.
      Exercise for diabetic pregnant women.
      • Meher S.
      • Duley L.
      Exercise or other physical activity for preventing pre-eclampsia and its complications.
      • Muktabhant B.
      • Lawrie T.A.
      • Lumbiganon P.
      • Laopaiboon M.
      Diet or exercise, or both, for preventing excessive weight gain in pregnancy.
      • Bain E.
      • Crane M.
      • Tieu J.
      • Han S.
      • Crowther C.A.
      • Middleton P.
      Diet and exercise interventions for preventing gestational diabetes mellitus.
      In fact, the contrary is true. There are lots of data that bed rest or decreased activity are harmful in pregnancy, with increased risks of venous thromboembolism, bone demineralization, and deconditioning.
      American College of Obstetricians and Gynecologists
      Physical activity and exercise during pregnancy and the postpartum period: Committee Opinion No. 650.
      Despite no evidence of benefit and known harms, bed rest continues to have wide use in obstetrics; approximately 15% of women each year are placed in best rest during their pregnancies in the United States.
      • Goldenberg R.L.
      • Cliver S.P.
      • Bronstein J.
      • Cutter G.R.
      • Andrews W.W.
      • Mennemeyer S.T.
      Bed rest in pregnancy.
      Seventy percent of Maternal Fetal Medicine physicians recommend bed rest for preterm labor (PTL), and 85% of them recommend bed rest in case of preterm premature rupture of membranes (PPROM),
      • Bigelow C.
      • Stone J.
      Bed rest in pregnancy.
      with no evidence of benefit. In fact, decreased activity is associated with increased risk of PTB in women at high risk for PTB, such as those with a short transvaginal ultrasound cervical length.
      • Grobman W.A.
      • Gilbert S.A.
      • Iams J.D.
      • et al.
      Activity restriction among women with a short cervix.
      Second, which women should exercise in pregnancy? The short answer is just about every pregnant woman should exercise in pregnancy. The American College of Obstetricians and Gynecologists (ACOG) lists absolute and relative contraindications to aerobic exercise in pregnancy.
      American College of Obstetricians and Gynecologists
      Physical activity and exercise during pregnancy and the postpartum period: Committee Opinion No. 650.
      To our knowledge, and as even ACOG implies, these are based perhaps on common sense, but none have been substantiated by data. For example, of the ACOG absolute contraindications to exercise in pregnancy, although some (hemodynamically significant heart disease, restrictive heart disease, severe anemia) seem reasonable, the others (cervical insufficiency or cerclage, multiple gestation, vaginal bleeding, placenta previa, PTL, PPROM, preeclampsia, and GHTN) actually may be situations in which some exercise may prove beneficial. We are not aware of level 1, or even good level II, evidence of harm from exercise in these situations. No evidence of fetal harm from exercise has been reported, with a 10–15 beats per minute increase in fetal heart rate (HR) during moderate-to-intense exercise and minimal decrease in birthweight from regular exercise during pregnancy and no increase in intrauterine growth restriction or small for gestational age.
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      • Kramer M.S.
      • McDonald S.W.
      Aerobic exercise for women during pregnancy.
      • Han S.
      • Middleton P.
      • Crowther C.A.
      Exercise for pregnant women for preventing gestational diabetes mellitus.
      • Ceysens G.
      • Rouiller D.
      • Boulvain M.
      Exercise for diabetic pregnant women.
      • Meher S.
      • Duley L.
      Exercise or other physical activity for preventing pre-eclampsia and its complications.
      American College of Obstetricians and Gynecologists
      Physical activity and exercise during pregnancy and the postpartum period: Committee Opinion No. 650.
      Third, what types of exercises should pregnant women do? Table 2 shows the types of exercises that have been studied in pregnancy in RCTs and found to be safe and associated with benefits (Table 1). Many other types of exercises are safe and beneficial, such swimming, jogging, running, yoga, pilates.
      American College of Obstetricians and Gynecologists
      Physical activity and exercise during pregnancy and the postpartum period: Committee Opinion No. 650.
      Examples of physical activities that have been listed as possibly unsafe include contact sports (eg, ice hockey, boxing), activities with high risk of falling (eg, skiing, horseback riding, sky diving), and scuba diving.
      American College of Obstetricians and Gynecologists
      Physical activity and exercise during pregnancy and the postpartum period: Committee Opinion No. 650.
      Some sports (eg, crew on an ergometer machine) may be deemed safe early in pregnancy but less feasible in the third trimester (personal communication, my rower son Andrea Berghella today while we were biking next to each other along the Schuylkill river in Philadelphia).
      Table 2Examples of types of exercises that have been extensively studied in pregnancy and found to be safe and beneficial
      Walking
      Stationary cycling
      Aerobic exercises
      Dancing
      Resistance (eg, weights, elastic bands) exercises
      Stretching exercises
      Hydrotherapy, water aerobics
      This is a partial list because the list of all safe and studied exercises in pregnancy would be too long to publish.
      Berghella. Exercise in pregnancy! Am J Obstet Gynecol 2017.
      Fourth, how much should pregnant women exercise? Most of the RCTs
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      • Kramer M.S.
      • McDonald S.W.
      Aerobic exercise for women during pregnancy.
      • Han S.
      • Middleton P.
      • Crowther C.A.
      Exercise for pregnant women for preventing gestational diabetes mellitus.
      • Ceysens G.
      • Rouiller D.
      • Boulvain M.
      Exercise for diabetic pregnant women.
      • Meher S.
      • Duley L.
      Exercise or other physical activity for preventing pre-eclampsia and its complications.
      that showed that exercise in pregnancy is safe and effective in producing benefits recommended starting aerobic exercise in the first trimester, with sessions lasting approximately 30–60 minutes, at least 3–4 times (up to daily) per week, until delivery (Table 3).
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      Many RCTs monitor maternal HR and suggest not exceeding a 60–80% of maximum HR threshold, which approximately means, as used in other RCTs, a maximum maternal HR of approximately 140 beats per minute. The Borg scale is a category scale that has been used to measure the level of perceived exertion to assess the intensity of exercise.
      • Borg G.A.
      Psychophysical bases of perceived exertion.
      RCTs and metaanalyses of RCTs on exercise in pregnancy have studied mainly “somewhat hard” or moderate-to-intense exercise regimens, which correspond to a Borg score of 13–14 (the scale is 6–20).
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      • Kramer M.S.
      • McDonald S.W.
      Aerobic exercise for women during pregnancy.
      • Han S.
      • Middleton P.
      • Crowther C.A.
      Exercise for pregnant women for preventing gestational diabetes mellitus.
      • Ceysens G.
      • Rouiller D.
      • Boulvain M.
      Exercise for diabetic pregnant women.
      • Meher S.
      • Duley L.
      Exercise or other physical activity for preventing pre-eclampsia and its complications.
      As recommended by ACOG and others,
      American College of Obstetricians and Gynecologists
      Physical activity and exercise during pregnancy and the postpartum period: Committee Opinion No. 650.
      Department of Health and Human Services
      2008 physical activity guidelines for Americans.
      women should be well hydrated before and during exercise, be able to carry a conversation during exercise (because this means they are likely not overexerting), and avoid lying flat on their backs for long periods.
      Table 3Characteristics of a safe and effective exercise regimen in pregnancy
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      • Kramer M.S.
      • McDonald S.W.
      Aerobic exercise for women during pregnancy.
      • Han S.
      • Middleton P.
      • Crowther C.A.
      Exercise for pregnant women for preventing gestational diabetes mellitus.
      • Ceysens G.
      • Rouiller D.
      • Boulvain M.
      Exercise for diabetic pregnant women.
      • Meher S.
      • Duley L.
      Exercise or other physical activity for preventing pre-eclampsia and its complications.
      When to startFirst trimester, <12 weeks gestation
      Duration of a session30-60 minutes
      Times per weekAt least 3–4 (up to daily)
      Intensity of exercise<60–80% of age-predicted maximum maternal heart rate
      Usually not exceeding 140 beats per minute
      Self-reported intensity of exercise (Borg scale)
      Borg scale is a 15-category scale (from 6–20) to measure the level of perceived exertion: light exercise is approximately 6–11; 13 is somewhat hard; 15 is hard; 19 is extremely hard.15
      Moderate intensity (12–14 on Borg scale)
      Supervision of exercisePreferred, if available
      When to endUntil delivery (as tolerated)
      Berghella. Exercise in pregnancy! Am J Obstet Gynecol 2017.
      a Usually not exceeding 140 beats per minute
      b Borg scale is a 15-category scale (from 6–20) to measure the level of perceived exertion: light exercise is approximately 6–11; 13 is somewhat hard; 15 is hard; 19 is extremely hard.
      • Borg G.A.
      Psychophysical bases of perceived exertion.
      Although the quality and extent of research on exercise in pregnancy is quite good, future research is needed. In particular, pregnant women who have been often excluded from RCTs in the past, such as those with previous PTB, multiple gestations, medical disorders (such as chronic hypertension, pregestational diabetes, cardiac disease, restrictive lung disease, renal disease, lupus, uncontrolled thyroid disease), those who experience complications such as short cervical length, PTL or PPROM, or GHTN or preeclampsia or those with ACOG absolute or relative contraindications to exercise
      American College of Obstetricians and Gynecologists
      Physical activity and exercise during pregnancy and the postpartum period: Committee Opinion No. 650.
      should be enrolled in future RCTs on exercise in pregnancy. Also, more level-1 evidence is needed on the effect of continuing strenuous exercise in elite athletes, which appears to be safe but has been insufficiently evaluated.
      • Bø K.
      • Artal R.
      • Barakat R.
      • et al.
      Exercise and pregnancy in recreational and elite athletes: 2016 evidence summary from the IOC expert group meeting, Lausanne. Part 2-the effect of exercise on the fetus, labour and birth.
      In summary, exercise is good for all of us nonpregnant adults, because it improves cardiorespiratory fitness, reduces the risk of obesity, enhances psychological well-being, and results in greater longevity.
      American College of Obstetricians and Gynecologists
      Physical activity and exercise during pregnancy and the postpartum period: Committee Opinion No. 650.
      Level-1 evidence now from >50 RCTs (including this new one by Wang et al
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      ) and several metaanalyses
      • Wang C.
      • Wei Y.
      • Zhang X.
      • et al.
      A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women.
      • Di Mascio D.
      • Magro-Malosso E.R.
      • Saccone G.
      • Marhefka G.D.
      • Berghella V.
      Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
      • Magro-Malosso E.R.
      • Saccone G.
      • Di Mascio D.
      • Di Tommaso M.
      • Berghella V.
      Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials.
      • Kramer M.S.
      • McDonald S.W.
      Aerobic exercise for women during pregnancy.
      • Han S.
      • Middleton P.
      • Crowther C.A.
      Exercise for pregnant women for preventing gestational diabetes mellitus.
      • Ceysens G.
      • Rouiller D.
      • Boulvain M.
      Exercise for diabetic pregnant women.
      • Meher S.
      • Duley L.
      Exercise or other physical activity for preventing pre-eclampsia and its complications.
      • Muktabhant B.
      • Lawrie T.A.
      • Lumbiganon P.
      • Laopaiboon M.
      Diet or exercise, or both, for preventing excessive weight gain in pregnancy.
      • Bain E.
      • Crane M.
      • Tieu J.
      • Han S.
      • Crowther C.A.
      • Middleton P.
      Diet and exercise interventions for preventing gestational diabetes mellitus.
      show that almost all pregnant women should exercise. Aerobic exercise (Table 2) is associated with important benefits, including less gestational weight gain; lower incidences of GDM, GHTN, GHTN disorders, PTB, and cesarean delivery; lower birthweight, and higher incidence of vaginal delivery (Table 1). To seize these benefits, aerobic exercise should be started in the first trimester and continued 3-4 times per week for 30- to 60-minute sessions each until delivery (Table 3). To stay inactive is to die.

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