Volume 86, Issue 11 p. 1290-1296
Free Access

Leisure time physical activity during pregnancy and impact on gestational diabetes mellitus, pre-eclampsia, preterm delivery and birth weight: a review

HANNE K. HEGAARD

Corresponding Author

HANNE K. HEGAARD

The Juliane Marie Centre, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark

Obstetric Clinic, The Juliane Marie Centre, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark

: Hanne K. Hegaard, JMC, Rigshospitalet-Panum, Section 3341, Blegdamsvej 9, DK-2100, Copenhagen Ø, Denmark [email protected]Search for more papers by this author
BENTE K. PEDERSEN

BENTE K. PEDERSEN

Centre of Inflammation and Metabolism at the Department of Infectious Diseases, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark

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BIRGITTE BRUUN NIELSEN

BIRGITTE BRUUN NIELSEN

Department of Obstetrics and Gynaecology, Aarhus University Hospital, Skejby, Denmark

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PETER DAMM

PETER DAMM

Obstetric Clinic, The Juliane Marie Centre, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark

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First published: 31 December 2010
Citations: 117

Abstract

Background. It has been questioned whether leisure time physical activity (LTPA) during pregnancy is beneficial or deleterious to pregnancy outcome, and whether a sedentary lifestyle during pregnancy has a negative impact on pregnancy. Answers to these questions are of general interest, since some young women are very physically active during leisure time, while others have a sedentary lifestyle. Method. In this review, we analysed the association between LTPA and the selected pregnancy outcomes, gestational diabetes mellitus (GDM), pre-eclampsia, preterm delivery, and birth weight. Results. The prevailing literature clearly indicates that LTPA before and/or during pregnancy has a protective effect on the development of GDM and pre-eclampsia. Furthermore, LTPA does not seem to have a negative impact on the rate of preterm delivery or on birth weight. Conclusion. Thus, it seems relevant that health authorities recommend 30 min of daily physical activity to healthy pregnant women.

Introduction

The impact of physical activity on public health in general has received significant focus and interest during the last decade. From the aspect of pregnant women, an increasing number of recent publications focus on the influence of leisure time physical activity (LTPA) during pregnancy. It has been questioned whether LTPA during pregnancy is beneficial or deleterious to pregnancy outcome, and whether a sedentary lifestyle during pregnancy has a negative impact on pregnancy. Answers to these questions are of interest, since some young women are very physically active during leisure time, while others have a sedentary lifestyle. A recent study shows that fewer women are physically active during their pregnancies than before their pregnancies, and that more than one-third are sedentary during pregnancy (1). The aim of this paper is to review the prevailing literature to describe the association between LTPA and gestational diabetes mellitus (GDM), pre-eclampsia, preterm delivery, and birth weight. Our review is primarily based on selected representative studies, since only a few meta-analyses exist on this topic. In this review, the term LTPA is used synonymous with exercise.

GDM complicates around 2–6% of pregnancies in European women (2), and is associated with significant maternal and perinatal morbidity and perinatal mortality (3, 4). Although glucose tolerance in most cases reverts to normal shortly after delivery, these women have a markedly increased risk of overt diabetes (mainly type 2 diabetes) in the future (5). It has been documented that treatment with diet, sometimes supplemented by insulin to normalise maternal glucose metabolism results in improved perinatal outcome (4). Hyperglycemia, insulin resistance, hyperlipidemia, low-grade inflammation and obesity characterise GDM (2). Outside pregnancy, physical activity has been shown to have a beneficial effect on all these factors (6, 7). The potential for prevention and treatment of GDM by physical activity, therefore, seems obvious. However, relatively few studies on this issue exist.

In a case control study of 155 women with GDM and 386 pregnant controls, Dempsey et al. (8) found that those participating in any LTPA during the first 20 weeks of pregnancy had an approximately 50% reduced risk of GDM (OR = 0.52, 95% CI: 0.33–0.80). The same authors (9) essentially confirmed their findings in a prospective cohort study of 909 normotensive, non-diabetic pregnant women. Any LTPA during the year prior to pregnancy was associated with a significantly reduced risk of GDM, while a non-significant risk reduction was found for any LTPA during the first 20 weeks of pregnancy (RR = 0.69, 95% CI: 0.37–1.29). Not surprisingly, the highest reduction was seen in women engaged in LTPA during both time periods (RR = 0.31, 95% CI: 0.12–0.79). Pregnant women, who were physically active >4.2 h per week in the year prior to pregnancy, experienced a 76% reduction in GDM (RR = 0.24, 95% CI: 0.10–0.64). In line with these findings, Zhang et al. (10), using the data from the Nurses’ Health Study II, recently found that LTPA, in particular vigorous activity, before pregnancy was associated with a significantly reduced risk for GDM. Of note is that in women not performing vigorous physical activities, brisk/very brisk walking was also associated with a significantly reduced risk (RR = 0.66, 95% CI: 0.46–0.95).

Another recent prospective cohort study of 1,805 women analysed the impact of physical activity before and during pregnancy on the development of either GDM or abnormal glucose tolerance during pregnancy (11). The clearest finding was that vigorous physical activity prior to pregnancy was associated with a reduced risk of 44% (OR = 0.56, 95% CI: 0.33–0.95) for GDM and 24% (OR = 0.76, 95% CI: 0.57–1.00) for abnormal glucose tolerance. During pregnancy, walking 2 h or more per week or light-to-moderate LTPA tended to reduce the risk of both GDM and abnormal glucose tolerance, although the findings were only of borderline statistical significance. Looking at pre-pregnancy and pregnancy physical activity at the same time, it was found that only the combination of vigorous physical activity before and vigorous or light to moderate activity during pregnancy had any protective effect for GDM (OR = 0.49, 95% CI: 0.24–1.01) and abnormal glucose tolerance (OR = 0.70, 95% CI: 0.49–1.01). Sub-analyses indicated that the effect of physical activity before pregnancy as well as during pregnancy was most marked for women with a prepregnancy BMI <25 kg/m2. This is in contrast to a large older study by Dye et al. (12), who found that physical activity during pregnancy reduced the risk of GDM significantly in women with a BMI >33 kg/m2 only (OR = 1.9, 95% CI: 1.2–3.1).

Thus, the evidence from observational studies clearly indicates that LTPA before and during pregnancy is associated with a reduced risk of GDM.

Pre-eclampsia

Pre-eclampsia is a leading cause of maternal and perinatal mortality and morbidity, and complicates around 4% of pregnancies in nulliparous women and 2% multiparous women, respectively (13, 14).

Little is known about whether the risk of pre-eclampsia can be modified by lifestyle changes. Pre-eclampsia is characterised by widespread endothelial dysfunction, insulin resistance, coagulation activation, and increased systemic inflammatory response (2), all typical findings in non-pregnant subjects with essential hypertension and type 2 diabetes. As mentioned previously, physical activity has a beneficial effect on these factors (6, 7), and it is, therefore, obvious to study the association between physical activity and the development of pre-eclampsia.

In a case control study with 201 cases (pre-eclampsia) and 383 controls (normotensive), Sørensen et al. (15) found that women engaged in any LTPA during early pregnancy had a 35% reduced risk of pre-eclampsia (OR = 0.65, 95% CI: 0.43–0.99) compared to sedentary women. Performing any LTPA the year prior to pregnancy as well as during early pregnancy was associated with a more marked reduced risk of pre-eclampsia. The risk of pre-eclampsia decreased with increasing intensity and amount of energy spent on physical activity. Pregnant women, spending 3.8–6.7 h per week on LTPA during the first 20 weeks of pregnancy, had a 68% reduced risk of pre-eclampsia (OR = 0.32, 95% CI: 0.56–0.66) compared to sedentary women. Another analysis from the same population looking at the perceived exertion during LTPA before pregnancy found an association between the relative intensity of physical activity and the risk reduction vis-à-vis pre-eclampsia (16). This association was present in both lean and overweight women. Women reporting strenuous to maximal exertion had a 78% reduction in the risk of developing pre-eclampsia.

Marcoux et al. showed similar results in an older case control study (17). They found a significantly reduced risk (RR = 0.67, 95% CI: 0.46–0.96) among pregnant women performing LTPA compared to inactive women. The reduction was attenuated with increasing intensity; energy expenditure of and time spent on LTPA. As an example, pregnant women performing more that 4 h LTPA weekly had a 40% reduction in pre-eclampsia (RR = 0.60, 95% CI: 0.38–0.95). In a nested case control study with only 44 women with pre-eclampsia, Saftlas et al. (18) found very similar risk reductions, although not statistically significant. A recent Cochrane review concluded that due to only a few and small randomised studies, it was not possible to come up with any final conclusions on the effect of LTPA on the risk of pre-eclampsia (19). However, the evidence from observational studies clearly indicates that LTPA before and during pregnancy is associated with a reduced risk of pre-eclampsia.

Preterm delivery

The rate of preterm delivery, a major determinant of neonatal mortality and morbidity, (20, 21) has increased in recent years (22, 23). From a public health perspective it is important to know whether factors, such as those related to lifestyle, influence preterm delivery. Studies on the association between LTPA and the risk of preterm delivery have been few (24–29). Irrespective of the definition of LTPA, no study found LTPA to be associated with an increased risk of preterm delivery.

In a case-control study (24) with 175 cases and 313 controls, Berkowitz et al. found that pregnant women participating in LTPA halved their risk of delivering preterm (OR = 0.53, 95% CI: 0.36–0.78) compared to less active women. These results are supported by other studies (26, 28).

In a follow-up study (29) of 557 pregnant women, the association between weekly average energy expenditure during LTPA and risk of preterm delivery was examined. Physical activity level was categorised as any physical activity, low-moderate (defined as <1,000 kcal of energy expenditure weekly) and heavy LTPA (defined as >1,000 kcal of energy expenditure weekly). Low-moderate LTPA was not associated with preterm delivery, while women performing heavy LTPA had a reduced risk of preterm delivery (OR = 0.11, 95% CI: 0.02–0.81). An expenditure of 1,000 kcal represents the equivalent of 3 h or more per week of high-impact aerobics or swimming and 5 h or more of bicycling.

Evenson et al. (25) examined the association between vigorous LTPA during the first and second trimester and the risk of preterm delivery, in a prospective study with 1,699 women. Vigorous LTPA was defined as, for example, aerobic exercise, jogging, lap swimming, and moderate to fast bicycling two times a week. Women performing vigorous LTPA during the first or second trimester did not have an increased risk of preterm delivery (OR = 0.80, 95% CI: 0.48–1.35 and OR = 0.52, 95% CI: 0.24–1.11). No association between hours spent on vigorous exercise and risk of preterm delivery was found.

Thus, the evidence from observational studies does not show that LTPA during pregnancy is associated with an increased risk of preterm delivery – in fact some studies point towards the reverse.

Birth weight

Birth weight is an important predictor of survival and health. Infants with a low birth weight (<2,500 g) have increased risk of perinatal morbidity and mortality, as well as adulthood hypertension and type 2 diabetes (30–34). However, delivering an infant with a birth weight >4,000 g increases the risk of other complications, such as shoulder dystocia, operative delivery, and birth canal lacerations (35). Furthermore, it has been associated with increased risks of certain types of diseases in adulthood, e.g. type 2 diabetes and in women breast cancer (36–38).

For many years, it has been questioned whether maternal LTPA during pregnancy affects birth weight. As the redistribution of blood flow to working muscles during physical activities might reduce placental circulation, thereby theoretically compromising fetal growth (39), many studies have focused on the potential adverse effects of LTPA on birth weight. However, it is difficult to compare results from the available studies, since the intensity, frequency and duration of the LTPA differ greatly. Three different meta-analyses have examined the association between LTPA and birth weight. Based on 18 studies, Lokey et al. (40) found no difference in birth weight for the infants of women who exercised below or above an intensity of <140 heart beats per minute. A recent Cochrane meta-analysis (41), based on 11 randomised studies involving 472 women, concluded that the available data were insufficient to infer any important risks or benefits on the mother and infant. The third meta-analysis by Leet and Flick (42) included the LTPA level before pregnancy, how far in pregnancy the women continued LTPA, and the types of control groups used for comparisons in the analyses. The conclusion was that exercise in pregnancy normally does not affect birth weight. However, it was found that vigorous endurance exercise during the third trimester was associated with a 200–400 g lower birth weight when compared with offspring of less physically active women. The highest weight reduction in this meta-analysis (42) was found in small studies on selected women (43–45), where confounding factors were not taken into account, making generalisation from these studies questionable. Some authors discuss if this reduction in birth weight was caused by inadequate energy consumption during and after LTPA and not by the LTPA per se (46, 47). Furthermore, the clinical relevance of this reduction in birth weight has also been discussed (42). If, for example, the reduction was found in the whole range of birth weight, this would mean that more small gestational age infants would be born, while on the other hand, it could be an advantage if it was more or less concentrated to infants with a high birth weight. In line with other studies, this indicates that a reduction in birth weight for large infants could be beneficial, and may reduce birth complications and the need for operative deliveries (48, 49).

The impact of vigorous LTPA in late pregnancy was evaluated in 61 physically active women randomised to continue with either 3 or 5 times per week of 30-min vigorous physical activity during the third trimester. The birth weights were the same in the 2 groups.

Many pregnant women are sedentary (1), thus it is relevant to focus on the impact of initiation of LTPA in these women. Some studies have examined the effect on birth weight in sedentary pregnant women beginning LTPA during pregnancy (51, 52). In a study by Clapp (51), 46 sedentary women were enrolled prior to pregnancy and randomly assigned at 8 weeks to a ‘no exercise’ group or an exercise group. Women in the exercise group performed 1–3 types of weight-bearing exercises (treadmill, step-aerobics or star stepper) for 20 min 3–5 times per week for the remainder of the pregnancy. The intensity was between 55 and 60% of the preconception maximum aerobic capacity. Women in the exercise group (n = 22) gave birth to children who were significantly heavier, longer and with a higher lean body mass. Another study indicates that regular LTPA modifies placental development, primarily in early and mid-pregnancy (53).

From the prevailing literature, it seems fair to conclude that physically active women can continue with LTPA during pregnancy without negative impact on birth weight. However, very active women performing LTPA at high intensity and frequency might be advised to reduce the activity level somewhat, since the literature does not clearly define a safe upper limits for LTPA. Furthermore, it is indicated that sedentary women can start LTPA during pregnancy without negative impact on offspring birth weight.

Strength conditioning

Although many young women participate in LTPA involving weight lifting and strength conditioning, there are not many studies in the literature on this subject. Therefore, the study by Hall and Kaufmann (54) will be described in detail. In total, 845 women were included in early pregnancy with the option of participating in an exercise program designed specifically for pregnant women. The exercise prescription included three components: (1) treadmill or bicycle warm up for 5 min, (2) use of selected exercise machines, (3) a 1- to 2-mile aerobic work-out on exercise bicycles until heart rate was 140 beats/min. The total exercise duration averaged 45 min, and the amount of resistance in the machines was individually adjusted. The women were asked to exercise 3 days per week until delivery. According to the number of exercise sessions completed during the pregnancy, they were categorised as control subjects (n = 393) with a mean of 0.8 sessions (range: 0–10), low-exercise group with 15 sessions (range: 11–20), medium-exercise group (n = 309) with 32 sessions (range: 21–59), and high-exercise group (n = 61) with 64 sessions (range: 60–99). Pregnancy outcomes were more favourable in the exercise groups, particular the high-exercise group. Significant data included shorter length of hospitalisation, lower rates of caesarean section and higher Apgar scores, and all women reported positive subjective responses to the exercise program. Fetal heart rates were monitored during LTPA at 28 weeks’ gestation and again 10 weeks later, and no incidence of fetal bradycardia was observed. Nevertheless, it is relevant to mention that the study was not randomised, and that the 4 groups were formed by self-selection.

Avery et al. (55) evaluated the cardiovascular response to maternal strength conditioning exercises in late pregnancy, and found that the blood pressure response during leg press in the third trimester was similar to what is seen outside pregnancy. Strength conditioning in the seated postures was associated with a significantly increased frequency of fetal heart rate accelerations, while strength conditioning in the supine postures (30° tilt) was associated occasionally with fetal bradycardia. The study suggested that the supine postures should be avoided during pregnancy.

These limited numbers of studies indicate that strength conditioning can be performed safely during pregnancy, but until further knowledge is available, the supine posture should be avoided during strength conditioning.

Conclusion

The numbers of studies on LTPA are limited, and the definitions used to classify intensity, amount and type of physical activity vary considerably, making comparisons between studies difficult. Furthermore, the actual number of cases in the majority of studies is rather low, thus hampering solid conclusions. However, the prevailing literature clearly indicates that LTPA before and/or during pregnancy has a protective effect on development of GDM and pre-eclampsia. This effect seems to increase with increasing intensity of and time spent on the physical activity. As regards the impact of LTPA on preterm delivery, observational studies show a reduced or unchanged risk in active pregnant women. However, since the studies were not randomised, the possibility of ‘a healthy woman effect’ is possible. Earlier, the literature focused on a potential deleterious effect of LPTA on birth weight based on theoretical considerations, but the current literature does not support this notion.

Pregnant women are generally highly motivated to follow advice to improve the outcome of pregnancy, and pregnancy should be an ideal time in life to focus on a healthy lifestyle. Many women will not come back to their pre-pregnancy weight after pregnancy, and physical activity during pregnancy might help preventing weight retention after pregnancy. This could be of utmost importance, since weight retention after pregnancy is associated with a poorer outcome in subsequent pregnancies (56), and with later obesity. In addition, overweight and obese women are at increased risk of several pregnancy complications, such as gestational hypertension, pre-eclampsia, GDM, fetal growth abnormalities, such as macrosomia and intrauterine growth restriction, stillbirth, congenital malformations and operative delivery (57–59). Finally, a healthier lifestyle continued after pregnancy might also reduce the increased risk of diabetes in women with previous GDM and of cardiovascular disease in women with previous GDM or pre-eclampsia.

In conclusion, this review found that women performing LTPA during and/or before pregnancy had a better or unchanged outcome in relation to GDM, pre-eclampsia, preterm delivery and birth weight. Importantly, there was no indication that physical activity in healthy pregnant women is associated with an increased risk of poor pregnancy outcome (60). Lastly, LTPA has been linked to improvements in physical fitness, emotional well-being and reduction in stress and anxiety.

Based on current knowledge, recent American recommendations state: ‘In the absence of either medical or obstetric complications, 30 minutes or more of moderate exercise a day on most, if not all, days of the week is recommended for pregnant women’ (60). This is in line with new Danish recommendations (Danish National Board of Health 2004) which state: ‘Pregnant women with a normal pregnancy should have at least 30 minutes of daily moderate physical activity. Women at risk of pre-eclampsia or gestational diabetes should be even more active’ (60).

However, we need well-planned clinical intervention trials to study various forms of physical activity and different intensity levels. Also, we need clinical trials to study whether different regimens should be followed by pregnant women in general, and by women at risk of, e.g. GDM and pre-eclampsia, respectively. Since more than one-third of pregnant women are sedentary, new studies should focus on how we can motivate these pregnant women to be physically active and follow the general recommendations (60, 61).