Matern Child Health J DOI 10.1007/s10995-013-1426-3

The Association Between Physical Activity and Maternal and Neonatal Outcomes: A Prospective Cohort Lisa M. Currie • Christy G. Woolcott • Deshayne B. Fell • B. Anthony Armson Linda Dodds



Ó Springer Science+Business Media New York 2013

Abstract Some evidence, but not enough to be conclusive, suggests that physical activity in pregnancy reduces the risk of perinatal complications. Our objective was to examine if physical activity in the year before pregnancy and in the first half of pregnancy is associated with maternal and neonatal outcomes. Associations between physical activity and maternal and neonatal outcomes were examined in a prospective cohort (n = 1,749) in Halifax, Canada. The Kaiser Physical Activity Survey, completed at approximately 20 weeks’ gestation, requested information regarding physical activity during the year before the pregnancy and the first 20 weeks of pregnancy. Outcomes were assessed by medical chart review. Multiple logistic regression was used to estimate odds ratios (OR) with 95 % confidence intervals (CI). Women with prepregnancy physical activity levels in the middle and highest tertiles were more likely to have high gestational weight gain relative to women in the lowest tertile [OR (CI): 1.40 (1.06–1.85) and 1.57 (1.18–2.09),

Electronic supplementary material The online version of this article (doi:10.1007/s10995-013-1426-3) contains supplementary material, which is available to authorized users. L. M. Currie  C. G. Woolcott (&)  L. Dodds Departments of Obstetrics and Gynaecology and Pediatrics, IWK Health Centre, Dalhousie University, 5980 University Ave., PO Box 9700, Halifax, NS B3K 6R8, Canada e-mail: [email protected] D. B. Fell Better Outcomes Registry and Network (BORN) Ontario, Children’s Hospital of Eastern Ontario Research Institute, Ottawa, ON, Canada e-mail: [email protected] B. A. Armson Department of Obstetrics & Gynaecology, Dalhousie University, Halifax, NS, Canada

respectively]. Higher physical activity in the first half of pregnancy decreased the odds of delivering a macrosomic infant (p trend = 0.005). Associations were not observed between total physical activity and gestational diabetes, gestational hypertension, pre-eclampsia, preterm birth, and low birth weight. Physical activity before, but not in the first half of pregnancy, is associated with high gestational weight gain. Physical activity in the first half of pregnancy may reduce the occurrence of macrosomia without affecting preterm birth or low birth weight. Keywords Exercise  Gestational diabetes  Pre-eclampsia  Gestational weight gain  Birth weight

Introduction Physical activity is an essential component of healthful living across the lifespan. Guidelines in Canada, the United Kingdom, the United States, and elsewhere recommend that physical activity be incorporated during pregnancy provided that no contraindications are present and that minor modifications are made (e.g. avoiding supine activities and activities that risk abdominal trauma) [1–4]. Although contraindications to physical activity in pregnancy are uncommon, a number of studies in diverse populations have documented that while physical activity levels are low before pregnancy, they fall even lower during pregnancy [5, 6]. This reduction in physical activity is problematic as it may lead to the loss of muscular and cardiovascular fitness among other things [1]. Consensus reviews of research done for the development of guidelines regarding physical activity in pregnancy have suggested that physical activity has the potential to reduce the risk of many complications of pregnancy [1];

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noted, however, was that not enough evidence exists to be conclusive [1]. Therefore, the objective of this study was to examine the association of physical activity in the year before pregnancy and in the first half of pregnancy with outcomes in pregnant women [gestational diabetes mellitus (GDM), gestational hypertension, pre-eclampsia, inappropriate gestational weight gain (GWG)] and newborns [preterm birth, low birth weight (LBW), macrosomia].

Methods Study Design and Participants This study examined a prospective cohort of pregnant women established at the Izaak Walton Killam (IWK) Health Centre in Halifax, Nova Scotia, Canada from October 2002 to July 2005. The original study was designed to determine the association between homocysteine, a risk factor for vascular disease, and pre-eclampsia [7]. Since detailed information about sociodemographic factors, lifestyle behaviours, previous pregnancies, and physical activity was collected by questionnaire at approximately 20 weeks of gestation and information about many perinatal outcomes was derived from medical chart review and a population-based perinatal database, these data were used to address the present objective. Participation (Supplementary Fig 1) was requested from 2,314 women who presented to have their blood drawn for routine screening between 4 and 19 weeks of gestation [median (interquartile range): 16.0 weeks (11.0 to 16.0)]. Of the 2,200 women who consented to participate, 153 were excluded (3 were [20 weeks gestation at recruitment, 8 with pre-existing diabetes, 21 with a higher order pregnancy, 94 had early pregnancy loss, 16 terminated their pregnancy, and 11 withdrew). We further excluded 289 women with missing information (33 did not return a questionnaire, 24 with unknown body mass index (BMI) or education, and 32 with missing outcome information). Finally, 9 women were excluded who had contraindications to physical activity present before 20 weeks gestation as defined by the Society of Obstetricians and Gynaecologists of Canada guidelines (SOGC) [1] (three had preterm labour or incompetent cervix requiring hospital admission and six had either preexisting or early onset hypertension requiring medication). Thus, 1,749 women were included in the main analysis. All women who participated provided written consent. The IWK Research Ethics Board approved all aspects of the study (file 2273). Physical Activity Assessment The questionnaire completed at approximately the 20th week of pregnancy requested information regarding

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physical activity during the year before pregnancy and in the first 20 weeks of pregnancy. Physical activity was assessed using the Kaiser Physical Activity Survey (KPAS), an instrument that has been validated in a pregnant population [8, 9]. Physical activity was assessed in four domains: active living, including active transport and a decrement for television watching (4 items); household/ caregiving activity, including cleaning and meal preparation (11 items); sports/exercise activity, including perceived fitness, sweating as an indicator of exertion, and volume of the three most frequent activities taking into account duration and intensity (up to 15 items); and occupational activity, reflecting job-related demands, such as standing or lifting (11 items). The score of each KPAS domain ranged from 1 to 5. The main exposure of interest, total KPAS score, was calculated as the sum of the three KPAS domain scores (active living, household/caregiving, sports/exercise), with possible values ranging from 3 to 15 [10]. Occupational activity was assessed only in the first 20 weeks of pregnancy and was omitted from the main analysis. Since the total KPAS scores with and without occupational activity were highly correlated (Pearson r = 0.86), the results using the score with all four domains of activity, shown in Supplementary Tables 1 and 2, were similar to the results shown herein. Outcome Data After delivery, outcome information was derived from medical chart review and linkage to the provincial Atlee Perinatal Database into which data from standardized clinical forms are entered by trained coders. The Reproductive Care Program of Nova Scotia administers the database and ensures its quality, integrity and security. An ongoing data quality assurance program shows that the data are accurate and reliable [11]. The maternal outcomes assessed were GDM, gestational hypertension, pre-eclampsia and GWG. In Nova Scotia, women without pre-existing diabetes are routinely screened for GDM between 24 and 28 weeks or earlier if risk factors are present. GDM was diagnosed according to SOGC guidelines [12]: 1-h plasma glucose [10.3 mmol/L in a 50 g glucose challenge test; in those women with 1-h plasma glucose between 7.0 and 10.3 mmol/L in the 50 g glucose challenge test, then fasting plasma glucose C 7.0 mmol/L, or two of fasting plasma glucose between 5.3 and 6.9 mmol/L, 1-h plasma glucose C 10.6, or 2-h plasma glucose C 9.2 mmol/L in an oral glucose tolerance test. Gestational hypertension, based on Canadian Hypertension Society criteria [13], was defined as diastolic blood pressure C 90 mmHg on two or more readings done at least 4 h apart after 20 weeks of gestation without proteinuria and no history of prepregnancy hypertension. Pre-

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eclampsia was similarly defined except with proteinuria present. Gestational weight gain outcomes were based on the ranges recommended by the Institute of Medicine [14] and Health Canada [15] that depend on a woman’s prepregnancy BMI: BMI \ 18.5 kg/m2 [12.5–18 kg]; BMI 18.5–24.9 kg/m2 [11.5–16 kg]; BMI 25.0–29.9 kg/m2 [7–11.5 kg]; and BMI C 30.0 kg/m2 [5–9 kg]. Gestational weight gain was missing for 362 participants. The neonatal outcomes assessed were preterm birth (\37 weeks’ gestation), LBW (\ 2,500 g) and macrosomia ([4,000 g). Gestational age was confirmed using ultrasound estimates and last menstrual period [7]. Small for gestational age (\10th percentile of sex- and gestational age-specific birth weight [16]) and large for gestational age ([90th percentile) were also investigated but the results were very similar to the results for LBW and macrosomia, respectively, and therefore, are not shown. Birth weight information was missing for one infant. Statistical Analysis Characteristics of the cohort participants were summarized with means and standard deviations for continuous factors and frequencies for categorical factors. Whether the distribution of these characteristics was different by level of physical activity was examined with Chi square tests and analysis of variance as appropriate. Logistic regression was used to assess the relationship between physical activity and birth and maternal outcomes. Odds ratios (ORs) and 95 % confidence intervals (CIs) were estimated. Physical activity scores from the KPAS were represented as tertiles based on the distribution in the entire cohort. Due to their known associations with the outcomes of interest, all models were adjusted for maternal age (\25, 25–35, [35 years) and prepregnancy BMI (\18.5, 18.5–24.9, 25–29.9, C30 kg/m2). Adjustment was also made for other covariates that were confounders in these data; in other words, covariates were included if, when entered in the models, a 5 % or greater change was observed in the ORs for the association between the total KPAS score in the first half of pregnancy and any of the outcomes. The covariates assessed were education (no university, university), marital status (married or common-law, single), smoking during pregnancy (no, yes), parity (nulliparous, parous), and employment during pregnancy (no, yes). Education and parity fit the criterion for inclusion. Additionally, previous history of GDM (no, yes) was included in the model with GDM as the outcome, and gestational age (continuous) was included in models of GWG, LBW, and macrosomia. Models of LBW and macrosomia were analyzed with and without adjustment for GWG to determine the possibility that it mediated their relationship with physical activity. Trend tests were completed by treating the physical activity

scores in tertiles as ordinal variables in the regression models. The significance of the product term between BMI (\25, C25 kg/m2) and the total KPAS score in the models was used to test for effect modification. All models of gestational hypertension were restricted to cohort participants who did not develop pre-eclampsia and vice versa. The analyses of high and low GWG, LBW and macrosomia were repeated among term births (gestational age between 37 and 42 weeks). All analyses were done using SAS version 9.2 (SAS Institute, Cary, NC). Statistical tests were two-sided with a 0.05 level of significance.

Results The 1,749 women completed the KPAS at a mean ± SD of 21.4 ± 3.7 weeks of gestation. Their demographic characteristics are described in Table 1. The mean age was 31 years, 49 % were nulliparous, and 41 % had a prepregnancy BMI of 25 kg/m2 or higher. Higher levels of physical activity in pregnancy were associated with higher maternal age and proportion married and university educated, and lower proportion of overweight or obesity, smoking and nulliparity. Maternal Outcomes The associations with maternal outcomes are shown in Table 2 for total physical activity score and in Supplementary Table 1 for physical activity in separate domains (active living, household/caregiving, sports/exercise). Point estimates of the ORs were suggestive of a protective effect of total physical activity in the upper relative to the lowest tertile, both before and in the first half of pregnancy, on the development of GDM. Due to the low number of cases, the 95 % CIs were imprecise and included the null values. When activity-specific domains were examined, relative to the lowest tertile of prepregnancy household physical activity, women within the middle and the highest tertiles were at decreased risk of GDM [OR (CI): 0.29 (0.12–0.74) and 0.33 (0.12–0.88), respectively]. Point estimates were also suggestive of a protective effect of both prepregnancy and pregnancy total physical activity on the development of gestational hypertension and pre-eclampsia but ORs and trend tests were not significant. Associations between physical activity and these maternal outcomes were not significantly modified by prepregnancy BMI. Gestational weight gain was associated with physical activity before pregnancy, but not in the first half of pregnancy (Table 2 and Supplementary Table 1). Relative to women with prepregnancy physical activity in the lowest tertile, women in the middle and highest tertiles were more likely to have high GWG (p trend = 0.002). The association

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Matern Child Health J Table 1 Descriptive characteristics of the cohort and according to category of physical activity in the first half of pregnancy (n = 1,749) Characteristic

All women n = 1,749

Tertile of physical activity in pregnancy (Total KPAS score) T1 (\6.44) n = 580

T2 (6.44–\7.97) n = 584

T3 (C7.97) n = 585

\25

9.3

10.0

12.5

5.3

25–35 [35

72.6 18.2

75.7 14.3

68.7 18.8

73.3 21.4

Married or common-law

91.1

91.2

88.0

94.0

\0.01

University educated

61.8

54.8

57.0

73.5

\0.01

Employed in pregnancy

85.6

87.6

83.4

86.0

p value \0.01

Maternal age (years)

0.12

Prepregnancy BMI (kg/m2)

\0.01

\18.5

3.7

3.9

3.6

3.6

18.5–24.9

55.7

49.4

55.5

61.9

25–29.9

22.2

23.6

22.9

20.5

18.4

23.1

18.1

14.0

Smoking in pregnancy

C30

14.9

18.1

17.1

9.4

\0.01

Nulliparous

49.3

56.7

46.6

44.6

\0.01

History of GDM

1.4

1.1

1.9

1.4

0.47

History of preterm delivery

5.7

4.6

6.5

6.0

0.36

Gestational age (weeks)

39.0 ± 1.9

39.0 ± 2.0

39.0 ± 1.9

39.0 ± 1.9

0.87

Data are expressed as a (column) percentage, with the exception of gestational age, expressed as the mean ± SD BMI body mass index, GDM gestational diabetes mellitus, GWG gestational weight gain, KPAS Kaiser Physical Activity Survey

Table 2 The association between total physical activity and maternal outcomes (n = 1,749) Tertile (total KPAS score)

Cohort

GDM

n

n

Adjusteda OR (95 % CI)

Gestational hypertension n

Adjustedb OR (95 % CI)

Pre-eclampsia N

Adjustedb OR (95 % CI)

Low GWG n

Adjustedc OR (95 % CI)

High GWG n

Adjustedc OR (95 % CI)

Prepregnancy T1 (\7.72)

566

16

1.00

42

1.00

25

1.00

61

1.00

250

1.00

T2 (7.72–\9.39)

599

12

0.71 (0.33–1.56)

41

0.91 (0.58–1.44)

20

0.80 (0.43–1.47)

44

0.62 (0.41–0.95)

303

1.40 (1.06–1.85)

T3 (C9.39)

584

8

0.60 (0.24–1.48)

23

0.61 (0.36–1.06)

14

0.68 (0.34–1.35)

56

0.70 (0.46–1.05)

276

1.57 (1.18–2.09)

p trend = 0.24

p trend = 0.09

p trend = 0.25

p trend = 0.08

p trend = 0.002

Pregnancy (1st half) T1 (\6.44) 580

14

1.00

49

1.00

23

1.00

44

1.00

293

1.00

T2 (6.44–\7.97)

584

15

1.08 (0.50–2.32)

28

0.59 (0.36–0.96)

21

1.08 (0.58–2.00)

62

1.39 (0.91–2.12)

266

0.94 (0.71–1.24)

T3 (C7.97)

585

7

0.56 (0.22–1.47)

29

0.67 (0.41–1.10)

15

0.83 (0.42–1.65)

55

1.07 (0.69–1.66)

270

0.99 (0.75–1.32)

p trend = 0.28

p trend = 0.09

p trend = 0.64

p trend = 0.81

p trend = 0.96

CI confidence interval, GDM gestational diabetes mellitus, GWG gestational weight gain, KPAS Kaiser physical activity survey, OR odds ratio a

Adjusted for maternal age, prepregnancy body mass index, education, parity, and history of GDM

b

Adjusted for maternal age, prepregnancy body mass index, education, and parity

c

Adjusted for maternal age, prepregnancy body mass index, education, parity, and gestational age

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between prepregnancy physical activity and the odds of high GWG was also observed with physical activity in the domains of active living (p trend = 0.03) and sports/exercise (p trend = 0.01). In the subgroup of term births, results were similar. The association between physical activity and GWG was not modified by prepregnancy BMI. Post hoc analyses were done to generate hypotheses about why GWG was associated with physical activity before pregnancy, but not in the first half of pregnancy, despite the two measures being moderately correlated (Spearman r = 0.68). Women who had higher physical activity scores before pregnancy reduced their activity levels more with pregnancy than women with lower activity levels. The median decrease in total KPAS score from the year before pregnancy to the first 20 weeks of pregnancy was 0.36, 1.08, and 1.59 among women in the first, second, and third tertiles of prepregnancy KPAS score, respectively (p \ 0.0001). For each unit decrease in KPAS score in the first half of pregnancy relative to before pregnancy, the odds of high GWG were elevated [OR (CI): 1.19 (1.08–1.30)]. Neonatal Outcomes The associations with neonatal outcomes are shown in Table 3 for total physical activity score and in Supplementary Table 2 for physical activity in the three component domains. No association was observed between physical activity and the risk of either preterm birth or LBW. Women with higher total KPAS scores in pregnancy were less likely to deliver a macrosomic infant (p trend = 0.005); KPAS scores specifically in the active living (p trend = 0.04) and household/caregiving domains (p trend = 0.04) were

significantly associated with macrosomia. A similar association was observed between prepregnancy household physical activity and macrosomia (p trend = 0.04). Further adjustment for GWG did not affect the association between physical activity and macrosomia. When the analysis of LBW and macrosomia was restricted to full term infants, results were unchanged. No significant interactions were found between total KPAS score and prepregnancy BMI in relation to these outcomes.

Discussion The findings of this prospective study of 1,749 pregnant women suggest that physical activity in the year before pregnancy and in the first half of pregnancy was not associated with many of the maternal and neonatal outcomes that were assessed. Gestational weight gain was positively associated with physical activity in the year prior to pregnancy but not in pregnancy. Physical activity in the first half of pregnancy, particularly active living and household activity, was related to a decreased occurrence of macrosomia. In the current study, physical activity during pregnancy was not associated with inappropriate GWG. Other cohort studies suggest that specific domains of physical activity could be related to a lower average GWG or a lower risk of excessive GWG including: household and caregiving activity [17]; walking [18, 19]; vigorous exercise [18]; total sport and recreational activities [18–20]; and steps per day [21]. On the other hand, in one study conducted in Hispanic women, sport and exercise activity and occupational activity were related to higher mean GWG [17]. When adjustment was made for covariates including

Table 3 The association between total physical activity and neonatal outcomes (n = 1,749) Tertile (total KPAS score)

Cohort

Preterm birth

LBW a

Macrosomia b

n

n

Adjusted OR (95 % CI)

N

Adjusted OR (95 % CI)

n

Adjustedb OR (95 % CI)

Prepregnancy T1 (\7.72)

566

39

1.00

23

1.00

96

1.00

T2 (7.72–\9.39)

599

35

0.84 (0.52–1.35)

15

0.54 (0.21–1.41)

88

0.75 (0.54–1.04)

T3 (C9.39)

584

43

1.06 (0.67–1.69)

27

1.45 (0.65–3.24)

93

0.90 (0.64–1.25)

p trend = 0.79

p trend = 0.35

p trend = 0.51

Pregnancy (1st half) T1 (\6.44)

580

34

1.00

22

1.00

T2 (6.44–\8.00)

584

43

1.31 (0.82–2.10)

25

1.20 (0.51–2.79)

89

0.74 (0.54–1.02)

T3 (C8.00)

585

40

1.17 (0.72–1.90)

18

0.88 (0.36–2.18)

77

0.61 (0.43–0.85)

p trend = 0.56

p trend = 0.76

111

1.00

p trend = 0.005

CI confidence interval, KPAS Kaiser physical activity survey, LBW low birth weight, OR odds ratio a Adjusted for maternal age, prepregnancy body mass index, education, and parity b

Adjusted for maternal age, prepregnancy body mass index, education, parity, and gestational age

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prepregnancy BMI, the observed associations were largely ameliorated in one study [17], but remained in another study [18]. Haakstad et al. [19] examined physical activity in each trimester and found a significantly reduced risk of gaining over 16 kg with physical activity in the last trimester, but no adjustment was made for maternal BMI. Some of the discrepancies between studies may be due to differences in methods of physical activity assessment, covariate adjustment, and population characteristics. No randomized controlled trial examining interventions on physical activity alone has found a significant effect [22, 23], but multifactorial interventions that also include diet and/or weight monitoring show a tendency toward slightly lower GWG [24, 25]. Only one other cohort study reported results for prepregnancy physical activity on GWG and found an association with lower weight gain in the third trimester [26] in contrast to the results of the current study in which prepregnancy physical activity was associated with excessive GWG. The post hoc analyses conducted herein suggest that the magnitude of the decrease in physical activity with the onset of pregnancy could contribute to excessive GWG. This hypothesis is supported by one small randomized controlled trial of aerobic exercise among active women; women randomized to an increase in duration from the first to the second half of pregnancy gained on average 2.5–3.5 kg less than women randomized to moderate duration throughout pregnancy or to a decrease in duration [27]. Since it has been shown repeatedly that women decrease their physical activity during pregnancy [5, 6], additional research is warranted paying particular attention to potential confounding by the reasons for a reduction in physical activity and the possible mediating effect of dietary compensation for altered physical activity patterns. Physical activity during pregnancy may reduce infant birth weight by limiting maternal positive energy balance, diverting blood and nutrients away from the placenta to the working muscles, and increasing maternal insulin sensitivity [28]. The effect on mean birth weight, however, has been generally small and inconsistent among both cohort studies and randomized controlled trials [20, 22, 25, 28–34]. A further question is whether the risk of extreme (low or high) birth weight is affected by physical activity. As in the current study, others have observed a lower occurrence of macrosomia [20, 32, 35] but no association [32] or a decreased risk of LBW or small for gestational age [20, 34, 36, 37]. Other cohort and case–control studies suggest that variation in pregnancy physical activity in the general population of developed countries is associated with either a null or protective effect on preterm birth [31, 38–40]. A meta-analysis of the five small randomized controlled trials conducted to date also suggests a null effect [RR (CI): 1.22 (0.51–2.90)] [34].

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With only 33 cases of GDM in the current study, the observed risk estimates that suggested a protective effect of total physical activity before and in the first half of pregnancy were not significant. Their magnitude, however, was consistent with risk estimates calculated from a recent meta-analysis of eight case–control and cohort studies [OR (CI): prepregnancy, 0.45 (0.28–0.75); pregnancy, 0.76 (0.70–0.83)] [41]. Similarly, our results show a nonsignificant trend toward a protective effect of physical activity against gestational hypertension and pre-eclampsia. Another small cohort study conducted in Hispanic women found a significantly protective effect of total physical activity in early pregnancy against hypertensive disorders [42]. Two large Scandinavian cohort studies that examined self-reported recreational physical activity, however, had conflicting results with one showing a protective effect against pre-eclampsia [43] and the other showing no effect against pre-eclampsia overall but an increased risk for severe subtypes [44]. A strength of the current study was that the assessment of physical activity used an instrument that has been validated in pregnant women [8] and included not only sport and leisure time exercise, but also active living and household activities to provide a more representative portrayal of activity levels. The role of activity in both the year prior to and the first half of pregnancy was considered. We accounted for important potential confounders of the relationship between physical activity and perinatal outcomes—social circumstances that afford the opportunity to be physically active and medical contraindications [40]— by adjusting for education level and excluding women with absolute contraindications to physical activity; nevertheless, residual confounding by these factors is possible. Information about another potential confounder, ethnicity or race, was not queried, but this factor would not be a strong confounder as the Nova Scotian population is [96 % Caucasian [45]. This study also had limitations. Physical activity—particularly that done in the year before pregnancy and in the second half of pregnancy—may have been subject to misclassification due to errors in recall and no further assessment, respectively. Misclassification would likely be nondifferential since exposure was reported before the occurrence of the outcomes, leading to an attenuation of the estimated associations. Occupational activity was not included although it could contribute a small amount of variability in physical activity between women [8]. The effects of very high physical activity could not be assessed as few women were at these levels (e.g. \6 % had total KPAS scores from 10 to 15). The potential impact of diet could not be assessed, thereby limiting the potential contribution of caloric intake on the study’s results. As noted by Althuizen et al. [46], elevated perceived food intake was associated with higher GWG. Further, dietary interviews

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and counselling in pregnancy have been associated with decreased prevalence of elevated GWG [47]. Although the cohort had 1,749 participants, the few cases of GDM, preeclampsia and LBW limited our statistical power. Finally, this study was not planned a priori to address the objectives of the present analysis. Rather, we took advantage of existing high quality data from a cohort in whom physical activity was assessed using a validated instrument and follow-up was complete. Many analyses were conducted but focussed on total physical activity and its association with outcomes that could be related to maternal obesity or energy balance; results on specific physical activity domains were offered as supporting information. Due to their interrelatedness, these analyses should not be viewed as independent. Examining main perinatal outcomes in concert provides an overall view of the benefits and risks of physical activity. Further study into other outcomes (e.g. depression, deep vein thrombosis, Caesarean section, neonatal intensive care admission, quality of life, health care costs) should be considered. Although randomized controlled trials may minimize confounding and other biases, in this context they are often limited by low adherence, examining select populations, and interventions only later in pregnancy. Observational studies, therefore, can contribute to the overall body of evidence. This study suggests that physical activity during the year before or in the first half of pregnancy does not affect the occurrence of preterm birth or LBW. However, physical activity in the first half of pregnancy appears to decrease the occurrence of macrosomia. On the whole, this evidence supports guidelines for physical activity in pregnancy as it may be associated with the reduction in risk of some adverse perinatal outcomes but not with an increased risk of others. As physical activity in the year prior to pregnancy, but not in the first half of pregnancy, was associated with excessive maternal GWG, further research should explore whether high prepregnancy physical activity or its reduction during pregnancy increases GWG. Acknowledgments This study was funded, in part, by a grant from the Canadian Institutes for Health Research (CIHR). CW is supported by an Izaak Walton Killam Establishment Grant. We are grateful for the assistance of the study coordinators, Adelia Trenchard and Anne Spencer. Conflict of interest conflicts of interest.

None of the authors have financial or other

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The association between physical activity and maternal and neonatal outcomes: a prospective cohort.

Some evidence, but not enough to be conclusive, suggests that physical activity in pregnancy reduces the risk of perinatal complications. Our objectiv...
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