obesity is a significant contributor to chronic disease worldwide.1 body size can be assessed using a variety of measures , including weight , height , and waist circumference . a widely utilized tool to assess overweight and obesity is body mass index ( bmi ) . the world health organization ( who ) defines normal weight as a bmi of 18.524.9 kg / m , overweight as a bmi of 2529.9 kg / m , and obesity as a bmi of 30 kg / m or greater.1 obesity is further subcategorized into class i ( 3034.9 kg / m ) , ii ( 3539.9 kg / m ) , and iii ( 40 kg / m or higher ) . australian data indicate that 63.4% of australian adults are overweight or obese , comprised of 35.0% overweight and 28.3% obese.2 it is predicted that by the year 2025 , 7.2 million australians will be obese.3 worldwide figures are similar . in the us , 66% of the population is overweight or obese.4 the most recent data from the uk show similar trends , with the prevalence of obesity increasing significantly from 13% to 25% between 1993 and 2008.5 china s national health survey also reported an increased prevalence of obesity , particularly among upper socioeconomic groups , with estimates that 11.44% of chinese youth are overweight or obese.6 overweight and obesity have significant implications during pregnancy and childbirth . in australia , it was estimated that 34% of pregnant women were overweight or obese in 2002.7 more recent population data from south australia indicate that approximately 50% of pregnant women are overweight or obese , including 10% who are severely or morbidly obese.8 figures from the us and the uk are similar . in the us , between 1993 and 2003 , the prevalence of maternal obesity increased from 13% to 22%,9 while there was a doubling in the uk between 1996 and 2006 , with approximately 27.5% of pregnant women overweight , and a further 10.9% obese.10 being overweight or obese may result in changes in hormone concentrations , adversely affecting reproductive health.11 obesity increases estrogen concentrations and hence the risk of menstrual dysfunction , polycystic ovarian syndrome , and infertility.12,13 both spontaneous rates of conception and outcomes following assisted reproductive techniques are poorer among women of high bmi when compared with women of normal bmi.12,13 the effect of obesity on risk of early pregnancy loss is less clear , with some studies reporting an increased risk of miscarriage , while others do not.13,14 it is well documented that even a moderate degree of weight loss can improve menstrual regularity and fertility among women who are overweight or obese.13 there are well - documented risks associated with obesity during pregnancy , the risks increasing with increasing maternal bmi.7,15,16 well - recognized risks include gestational diabetes , hypertensive conditions ( including preeclampsia ) , and preterm birth.7,15 there are also considerable risks for the infant , including an increased risk of perinatal death , congenital anomalies , shoulder dystocia , birth injuries , and macrosomia.7,15,17,18 the risks associated with overweight and obesity during pregnancy are summarized in table 1 . while the precise factors contributing to overweight and obesity are complex , these conditions essentially represent an imbalance between energy intake and energy expenditure . the total amount of energy an individual expends on a daily basis is a function of the amount of energy required to maintain basic bodily functions ( resting energy expenditure ) , digest food eaten ( thermic effect of food ) , maintain posture and spontaneous activity , and support voluntary bodily movement ( physical activity).19 reflecting its voluntary nature , physical activity is the most variable component of total daily energy expenditure . it comprises 20%30% of total energy expenditure in sedentary adults , and the proportion is notably higher among active individuals.19 domains of physical activity include leisure - time pursuits ( exercise ) , occupation , transportation , self - care , volunteer work , nonexercise leisure - time activities , and domestic - related activity.19 although each of these domains may have a significant influence on energy expended in physical activity and consequently total daily energy expenditure , until recently leisure - time physical activity was the focal point for research on energy expenditure in relation to obesity and public health efforts aimed at obesity treatment and prevention.19 the beneficial outcomes of being physically active are well recognized , including improving cardiovascular condition and glucose tolerance , building bone and muscle mass , and reducing risks of obesity and its complications.20,21 physical activity has been identified as an important factor for healthy pregnancy in women of all weight ranges . current australian physical activity guidelines suggest adults , including pregnant women , be active with moderate - intensity exercise for 30 minutes on most days.22 both the royal college of obstetricians and gynaecologists and american college of obstetricians and gynecologists recommend that all pregnant women be encouraged to participate in exercise , with an aim of maintaining fitness throughout pregnancy.23,24 while previously inactive women and women with pregnancy complications may benefit from exercise , recommendations suggest evaluation on an individual basis.24 it is important to recognize that these activity guidelines for pregnant women are based on low - level evidence , and do not specifically address the issues facing women who are overweight or obese . research over the past 25 years has generated a large amount of information about exercise during pregnancy . however , the evidence has not been summarized to provide a full story about the benefits of antenatal exercise , current physical activity patterns during pregnancy , and women s perception of exercise during pregnancy . the objective of this review was to provide a comprehensive overview of the effect of physical activity on pregnancy outcomes , the change of physical activity during pregnancy , and women s perception of being physically active during pregnancy , with a particular focus on women who are overweight or obese . many studies have investigated the effect of exercise during pregnancy and maternal and neonatal health outcomes . the search identified articles published in pubmed and scopus between 1990 and february 2013 using the following keywords :  exercise  or  physical activity  or  lifestyle  and  pregnancy  . the search resulted in 373 publications , of which the authors considered 81 after full - text review . as outlined in table 2 , although studies utilized different research designs , a beneficial effect of exercise during pregnancy on maternal and neonatal health outcomes has been consistently identified . in particular , maternal health benefits include reduced risk of gestational diabetes,2527 preeclampsia,2830 and operative birth,31 in addition to improved cardiovascular function,32 overall fitness,33 psychological well - being , and mood stability.34,35 benefits for the infant include reduced risks of prematurity36,37 and improved fetal growth,38 although there is more limited information about longer - term health benefits for both women and infants . however , these studies have limitations , including the inclusion of women of all bmi categories , failure to control for the effect of maternal bmi , and lack of standardization of methodology relating to assessment of physical activity , in addition to the limitations of specific study design . in addition , though a study that analyzed the intensity of physical activity during pregnancy suggested particularly beneficial effects from vigorous physical activity,30 it is difficult to draw conclusions , as studies ( see table 2 ) have utilized very different definitions43 to describe the intensity of exercise during pregnancy and are hence hard to compare . there are three relevant cochrane reviews relating to exercise in pregnant women.3941 kramer and mcdonald39 evaluated the role of exercise in pregnancy , while ceysens et al40 and han et al41 focused on exercise in women with gestational diabetes and the preventive effect of physical activity during pregnancy . kramer and mcdonald s cochrane review of aerobic exercise included women of all bmi categories during pregnancy , and included eleven randomized controlled studies , involving 1014 women.39 outcome measurements included maternal physical fitness , infant anthropometric measures , and adverse maternal and infant birth outcomes . the included trials varied considerably in the nature of the intervention provided , the timing and duration of the intervention , and the assessment of compliance . the sample sizes of the individual studies were relatively small , and all were considered to have methodological flaws . while regular exercise was associated with maintained or improved physical fitness ( defined as aerobic capacity , cardiopulmonary measures , and physical work capacity ) , the effect on clinical pregnancy outcomes was uncertain . ceysens and colleagues focused on exercise for women with gestational diabetes.40 the authors utilized data from four randomized controlled trials , involving a total of 114 pregnant women with gestational diabetes . the exercise programs generally included three 20- to 45-minute sessions per week of approximately 6 weeks duration . the meta - analysis did not identify a significant effect of exercise on measures of perinatal or maternal morbidity , although the available sample size was well underpowered to be able to detect differences in outcomes of clinical relevance . similarly , han and colleagues focused on the effect of physical activity in prevention of gestational diabetes.41 the findings indicated no significant differences in the incidence of gestational diabetes between women receiving additional exercise intervention and routine care . in the overweight and obese pregnant population , several systematic reviews and meta - analyses have assessed the effect of antenatal exercise interventions on pregnancy outcomes.4244 these meta - analyses of randomized trials indicate that while antenatal exercise interventions do not appear to be associated with harm , the effect on limiting gestational weight gain was moderate ( mean difference 0.36 kg , 95% confidence interval 0.64 to 0.09 kg , p = 0.008 , i2 = 0%43 ; mean difference 0.72 kg , 95% confidence interval 1.2 to 0.25 kg , p = 0.003 , i2 = 30%44 ) . however , the available evidence is limited by small sample sizes and lack of consistent reporting of clinically relevant outcomes . there is considerable literature indicating that pregnant women are less active than nonpregnant women , with activity declining over pregnancy.45,46 the existing literature examining physical activity patterns during pregnancy has generally focused on women of all bmi categories,4754 consistently indicating a reduction in activity over the course of pregnancy45 from early pregnancy to birth4952 ( table 3 ) . this decline in activity was apparent across all categories and intensity of activities ( household , leisure / exercise , work - related , and transportation).4952 the available literature evaluating physical activity during pregnancy among women who are overweight or obese is more limited . while some authors report an increase in activity from early to midpregnancy , followed by a decline in the third trimester,54 others report a constant reduction in activity across gestation53 ( table 3 ) . furthermore , there is little information reported in the literature evaluating the relationship between high maternal bmi and patterns of physical activity , in addition to the effect of gestational weight gain . a prospective survey by clarke and gross46 reported that the decline in physical activity during pregnancy might be explained by a variety of social and psychological factors , as women perceived resting and relaxation as significantly more important than maintaining an active lifestyle . major sources of information about physical activity advice included books , magazines , and family and friends , rather than health professionals . the findings of such studies indicate the importance of health professionals in improving the quantity and quality of health education about physical activity during pregnancy , including where possible the involvement of women s family and friends . while there are potential opportunities to implement interventions during pregnancy to improve health outcomes , success requires an understanding of women s attitudes and perceptions , particularly their willingness to make behavioral changes . while many interventions aim to promote healthy eating and active lifestyle in women who are overweight or obese during pregnancy,43,5557 it is constantly reported that adherence to interventions remains problematic . while a previous study has demonstrated that women s attitudes toward weight - control interventions during pregnancy are generally positive,58 there is an increasing need to recognize and address individual psychological aspects and the impact they may have on successful behavioral change.59,60 a number of studies have investigated women s perceptions of being active during pregnancy , identifying a number of enablers and barriers . as outlined in table 4 , these studies utilized a variety of tools , including self - reported questionnaires , telephone interviews with open - ended questions , focus groups , and semistructured face - to - face interviews , many utilizing mixed methods to gather both qualitative and quantitative data.46,6165 the most notable barriers identified preventing women from being active during pregnancy were pregnancy symptoms , lack of time , access to child care , and concerns about their safety and that of their unborn baby . conversely , significant enablers included positive psychological feelings , family influence , and receiving advice from health professionals . many of these studies are limited by their small sample size , and involved women of all bmi categories with no specific information available for pregnant women who were overweight or obese . there are few studies that have explored the beliefs and experiences of exercise among women who were overweight or obese during pregnancy . tovar et al s study involved four focus groups66 to evaluate knowledge and beliefs regarding weight gain during pregnancy among a group of hispanic women in the us . the results confirmed that while the majority of women felt negatively about weight gain , it was supported by family members in the belief that this would lead to a healthier baby . while women had awareness of the benefits of a healthy diet , traditional beliefs remained strong . weir et al evaluated beliefs about physical activity among overweight and obese pregnant women using semistructured interviews.67 overall , women considered healthy eating of greater importance for maternal and infant health than participation in physical activity . furthermore , while there was awareness that physical activity during pregnancy impacted on weight gain , women expressed a preference to defer weight management to the postnatal period . studies have identified a range of barriers preventing women from leading a healthier lifestyle during pregnancy , including physical , psychological , external , and environmental factors . in particular , a lack of advice was considered significant , with women expressing a lack of information relating to the benefits of physical activity on maternal and infant health . while most women who were overweight or obese recognized their weight as an issue , there was concern that health professionals in particular did not address women s individual expectations.68 our previous mixed - methods study in an overweight and obese pregnant population generated detailed information about women s views of making healthy diet and lifestyle changes during pregnancy.69 women completed questionnaires as well as a smaller number of face - to - face interviews , with results indicating that approximately half of women did not consider excessive gestational weight gain to be a concern during pregnancy . although many women were aware that high bmi and high gestational weight gain were associated with adverse maternal health outcomes , knowledge of neonatal outcomes was less evident , as were perceived benefits of healthy change . while a range of barriers to change were identified , the strongest motivator reported was concern about maternal and neonatal health . engaging in a healthy routine prior to conception , positive influences from family , and health professionals addressing individual expectations the extant literature indicates that while women accept the occurrence of weight gain as a outcome of pregnancy,70 they report receiving a lack of and often inconsistent information from health professionals about high bmi and associated pregnancy risks , and about exercise during pregnancy.66,67,70 in contrast , advice from family relating to optimal gestational weight gain and physical activity was considered to be highly influential.66 being overweight or obese during pregnancy is associated with an increased risk of maternal and infant health complications . while there are documented beneficial effects associated with exercise in pregnancy , recommendations to date are based on low - quality evidence and do not specifically address exercise in pregnancy for women who are overweight or obese . furthermore , little is known about women s perceptions of making healthy change during pregnancy . there is a need for a detailed description of physical activity patterns during pregnancy in women who are overweight or obese , and more randomized trials evaluating exercise interventions for women who are overweight or obese , with a focus on clinical outcomes . further research also needs to identify effective strategies to increase physical activity among women who are overweight or obese during pregnancy , particularly at an individualized level .
overweight and obesity have significant implications during pregnancy and childbirth . 
 the objective of this review was to provide a comprehensive overview of the effect of physical activity on pregnancy outcomes , the change of physical activity during pregnancy , and women s perception of being physically active during pregnancy , with a particular focus on women who are overweight or obese . 
 many studies have investigated the beneficial effect of exercise during pregnancy , including reduced risk of gestational diabetes , preeclampsia , and operative birth , in addition to improved cardiovascular function , overall fitness , psychological well - being , and mood stability . 
 benefits for the infant include reduced risks of prematurity and improved fetal growth , although there is more limited information about longer - term health benefits for both women and infants . 
 the existing literature examining physical activity patterns during pregnancy has generally focused on women of all body mass index categories , consistently indicating a reduction in activity over the course of pregnancy . however , the available literature evaluating physical activity during pregnancy among women who are overweight or obese is more limited and contradictory . 
 a number of studies identified barriers preventing women from being active during pregnancy , including pregnancy symptoms , lack of time , access to child care , and concerns about their safety and that of their unborn baby . 
 conversely , significant enablers included positive psychological feelings , family influence , and receiving advice from health professionals . 
 very few studies have provided insights about perceptions of being active during pregnancy in the overweight and obese population . 
 there is a need for a detailed description of physical activity patterns during pregnancy in women who are overweight or obese , and more randomized trials evaluating exercise interventions for women who are overweight or obese , with a focus on clinical outcomes .