Objective To perform a systematic review of the relationships between prenatal exercise and maternal harms including labour/delivery outcomes.
Design Systematic review with random effects meta-analysis and meta-regression.
Datasources Online databases were searched up to 6 January 2017.
Study eligibility criteria Studies of all designs were included (except case studies) if they were published in English, Spanish or French and contained information on the population (pregnant women without contraindication to exercise), intervention (subjective or objective measures of frequency, intensity, duration, volume or type of exercise), comparator (no exercise or different frequency, intensity, duration, volume and type of exercise, alone [“exercise-only”] or in combination with other intervention components [e.g., dietary; “exercise + co-intervention”]) and outcome (preterm/prelabour rupture of membranes, caesarean section, instrumental delivery, induction of labour, length of labour, vaginal tears, fatigue, injury, musculoskeletal trauma, maternal harms (author defined) and diastasis recti).
Results 113 studies (n=52 858 women) were included. ‘Moderate’ quality evidence from exercise-only randomised controlled trials (RCTs) indicated a 24% reduction in the odds of instrumental delivery in women who exercised compared with women who did not (20 RCTs, n=3819; OR 0.76, 95% CI 0.63 to 0.92, I 2= 0 %). The remaining outcomes were not associated with exercise. Results from meta-regression did not identify a dose–response relationship between frequency, intensity, duration or volume of exercise and labour and delivery outcomes.
Summary/conclusions Prenatal exercise reduced the odds of instrumental delivery in the general obstetrical population. There was no relationship between prenatal exercise and preterm/prelabour rupture of membranes, caesarean section, induction of labour, length of labour, vaginal tears, fatigue, injury, musculoskeletal trauma, maternal harms and diastasis recti.
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What is already known
Approximately 15% of births worldwide are by caesarean delivery (~5% in least developed countries and ~27% in more developed countries).
Compared with vaginal delivery, caesarean deliveries have increased risk of adverse maternal and fetal outcomes, delayed recovery and higher healthcare costs.
What are the new findings
Prenatal exercise reduced the odds of instrumental delivery by 24%.
Prenatal exercise did not affect preterm/prelabour rupture of membranes, caesarean section, instrumental delivery, induction of labour, length of labour, vaginal tears, fatigue, injury, musculoskeletal trauma, maternal harms and diastasis recti.
There was no evidence for a dose–response relationship between frequency, intensity, duration or volume of exercise and labour and delivery outcomes.
The impact of prenatal exercise on labour and delivery outcomes including preterm/prelabour rupture of membranes, caesarean section, instrumental delivery (forceps or vacuum), induction of labour, length of labour, vaginal tears, fatigue, injury, musculoskeletal trauma, maternal harms and diastasis recti is not well understood. Planned vaginal delivery is recommended in the absence of a threat to maternal or fetal health requiring interventions such as caesarean or instrumental delivery.1 2 Yet, approximately 15% of births worldwide are by caesarean delivery (5% in less developed and 27% in more developed countries).3 4 Although slow labour progression (resulting in prolonged labour and maternal fatigue) is a common indication for caesarean sections, elective caesarean deliveries are also on the rise.5 Compared with vaginal delivery, caesarean deliveries are associated with increased risk of adverse maternal and fetal outcomes, delayed recovery and higher healthcare costs.6–9
In response to rising rates of caesarean delivery, the American College of Obstetricians and Gynecologists (ACOG) released a position statement advocating for strategies to reduce the number of caesarean deliveries.5 One such strategy may be prenatal exercise as there is some evidence suggesting reduction in the risk of caesarean delivery.10 However, even vaginal deliveries can be associated with acute and chronic maternal morbidity, as instrumental deliveries and vaginal tears are associated with postpartum urinary incontinence.11 The impact of prenatal exercise on these outcomes is not well understood.
Some healthcare providers and patients are concerned that regular prenatal exercise may cause musculoskeletal injury or premature delivery.12 Although this has not been substantiated in women without contraindications to exercise, no systematic review that has examined specific concerns regarding labour and delivery outcomes.
The present meta-analysis was conducted as part of a series of reviews that will form the evidence base for the development of the 2019 Canadian guideline for physical activity throughout pregnancy (herein referred to as Guideline).13 The current review aimed to assess the associations between prenatal physical activity (in terms of frequency, intensity, type and volume of physical activity), with maternal harms, labour and delivery outcomes.
The Guidelines Consensus Panel including researchers, methodological experts, a fitness professional and representatives from the Society for Obstetricians and Gynecologists of Canada, Canadian Society for Exercise Physiology (CSEP), The College of Family Physicians of Canada, Canadian Association of Midwives, Canadian Academy of Sport and Exercise Medicine, Exercise is Medicine Canada and a representative health unit (the Middlesex-London Health Unit) assembled to identify priority outcomes for the Guideline update. The Guidelines Consensus Panel selected 20 ‘critical’ and 17 ‘important’ outcomes related to prenatal exercise and maternal or fetal health. Three of the ‘critical’ outcomes (ie, caesarean section, preterm/prelabour rupture of membranes and diastasis recti) were examined in this review. The remaining outcomes (instrumental delivery, induction of labour, length of labour, vaginal tears, fatigue, injury, musculoskeletal trauma and maternal harms) were rated as ‘important’. This systematic review and meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and the checklist was completed.14
Protocol and registration
Two systematic reviews were undertaken to investigate the impact of prenatal exercise on fetal and maternal health outcomes, and records identified through both processes were considered for inclusion in the current review. Each review was registered a priori with the International Prospective Register of Systematic Reviews (fetal health: CRD42016029869; maternal health: CRD42016032376). Because the relationships between prenatal exercise and birth complications were examined in studies related to both fetal and maternal health, records retrieved from both of these searches were evaluated for inclusion in the present review.
The participants, interventions, comparisons, outcomes and study design framework guided this review.15
The population of interest was pregnant women without contraindication to exercise (according to the CSEP and ACOG guidelines).12 16 Absolute contraindications were defined as: ruptured membranes, premature labour, persistent second or third trimester bleeding, placenta praevia, pre-eclampsia, gestational hypertension, incompetent cervix, intrauterine growth restriction, high order pregnancy, uncontrolled type 1 diabetes, hypertension or thyroid disease or other serious cardiovascular, respiratory or systemic disorders. Relative contraindications were defined as: a history of spontaneous abortion, premature labour mild/moderate cardiovascular or respiratory disease, anaemia or iron deficiency, malnutrition or eating disorder, twin pregnancy after 28 weeks or other significant medical conditions.12 16
The intervention/exposure of interest was objective or subjective measures of frequency, intensity, duration, volume or type of exercise. Prenatal exercise could be acute (ie, a single exercise session) or habitual (ie, usual activity). Interventions including exercise alone (termed ‘exercise-only’ interventions) or exercise combined with other interventions (eg, diet intervention or behavioural intervention, termed ‘exercise+cointerventions’) were considered. Exercise-only interventions could include standard care. If exercise began after the initiation of labour, then studies were not eligible for inclusion. Although exercise is a subtype of physical activity, for the purpose of this review, we used the terms interchangeably. Exercise and physical activity were defined as any bodily movement generated by skeletal muscles that resulted in energy expenditure above resting levels.17
Eligible comparators were: no exercise; different frequency, intensity, duration, volume and type of exercise; different duration of intervention; or exercise in a different trimester.
Relevant outcomes were preterm/prelabour rupture of membranes, caesarean section, instrumental delivery, induction of labour, length of labour, vaginal tears, fatigue, injury, musculoskeletal trauma, maternal harms (author defined) and diastasis recti.
Primary studies of any design were eligible, with the exception of case studies (n=1), narrative syntheses and systematic reviews.
A comprehensive search was created and run by a research librarian (LGS) in the following databases: MEDLINE, Embase, PsycINFO, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, Scopus and Web of Science Core Collection, CINAHL Plus with Full-text, Child Development & Adolescent Studies, ERIC, Sport Discus, ClinicalTrials.gov and the Trip Database up to January 6, 2017 (see online supplementary data for complete search strategies).
Study selection and data extraction
Two reviewers independently screened the titles and abstracts of all retrieved articles. Abstracts that were identified to have met the initial screening criteria by at least one reviewer were automatically retrieved as full-text articles. Full-text articles were then independently screened by two reviewers for relevant outcomes prior to extraction. For studies where at least one reviewer recommended exclusion, further review was conducted by MHD and/or S-MR for final decision on exclusion. In the event of a disagreement after further discussion, the study characteristics were presented to the Guidelines Steering Committee who oversaw the systematic reviews (MHD, MFM, S-MR, CEG, VP, AJG and NB) in order to come to a final decision regarding inclusion/exclusion by consensus. Studies identified by the maternal and fetal search strategies were imported into DistillerSR for deduplication and data extraction and were subsequently considered as one review.
Data extraction tables were created in DistillerSR in consultation with methodological experts and the Guidelines Steering Committee. Data from records that met the inclusion criteria were extracted by one person and independently verified by a content expert (MHD, MFM or S-MR). For studies where multiple publications exist, the most recent or complete publication was selected as the ‘parent’ paper; however, relevant data from all publications were extracted. Extracted data were study characteristics (ie, year, study design and country) and characteristics of the population (eg, number of participants, age, prepregnancy body mass index (BMI), parity and pregnancy complications including pre-eclampsia, gestational hypertension and gestational diabetes), intervention/exposure (prescribed and/or actual exercise frequency, intensity, time and type of exercise, duration of the exercise training and measure of physical activity) and outcomes (preterm/prelabour rupture of membranes, caesarean section, instrumental delivery, induction of labour, length of labour, vaginal tears, fatigue, injury, musculoskeletal trauma, maternal harms and diastasis recti) (see online supplementary table 1). If data were unavailable for extraction, authors were contacted to request additional information. Data that were only available in figures, the authors were initially contacted, and if there was no response, data were extracted by digitising graphs using GetData Graph Digitizer (V.2.26).18
The Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework was used to assess the quality of evidence across studies for each study design and health outcome.19
Accordingly, evidence from RCTs was considered ‘high’ quality and was graded down if there was concern with risk of bias,20 indirectness,21 inconsistency,22 imprecision23 or risk of publication bias,24 because these factors reduce the level of confidence in the observed effects. Evidence from all non-randomised intervention and observational studies was considered ‘low’ quality and, if there was no cause to downgrade, was upgraded, if applicable, according to the GRADE criteria (eg, large magnitude of effect and evidence of dose–response).25
Specifically, the risk of bias in RCTs and intervention studies were assessed following the Cochrane Handbook,26 and the risk of bias in observational studies were assessed using the characteristics recommended by Guyatt et al,20 consistent with systematic reviews conducted to support previous health behaviour guidelines.27 All studies (RCTs, intervention studies and observational studies) were assessed for potential sources of bias including selection bias (RCT/intervention: inadequate randomisation procedure; observational: inappropriate sampling), reporting bias (selective/incomplete outcome reporting), performance bias (RCT/intervention: compliance to the intervention; observational: flawed measurement of exposure), detection bias (flawed measurement of outcome), attrition bias (incomplete follow-up and high loss to follow-up) and ‘other’ sources of bias. Risk of bias across studies was rated as ‘serious’ when studies with the greatest influence on the pooled result (assessed using weight (%) given in forest plots or sample size in studies that were narratively synthesised) presented ‘high’ risk of bias. The greatest influence on the pooled result was determined as follows: the studies that had the greatest individual % contribution in the meta-analyses, when taken together, contributed to >50% of the weight of the pooled estimate. Additionally, studies were considered to reflect a serious risk of bias when sample size of narratively synthesised studies was similar to the total sample size of studies contributing to >50% of the weight of the pooled estimate in the meta-analyses. Given the nature of exercise interventions, it is not possible to blind participants to group allocation, and selection risk of bias was rated as ‘low’ if this was the only source of bias identified. Performance bias was rated as ‘high’ when <60% of participants performed 100% of prescribed exercise sessions or attended 100% of counselling sessions (defined as low compliance) or when compliance to the intervention was not reported. Attrition bias was rated as ‘high’ when >10% of data were missing at the end of the study and intention-to-treat analysis was not used.
Inconsistency across studies was considered serious when heterogeneity was high (I2 ≥50%) or when only one study was assessed (I2 unavailable). Indirectness was considered serious when cointerventions were included in the assessment of the outcome of interest. Imprecision was considered serious when the 95% CI crossed the line of no effect and was wide, such that interpretation of the data would be different if the true effect were at one end of the CI or the other. When only one study was assessed, imprecision was not considered serious as inconsistency was already considered serious for this reason. Finally, publication bias was assessed if possible (ie, at least 10 studies were included in the forest plot) via funnel plots (see online supplementary data). If there were fewer than 10 studies, publication bias was deemed non-estimable and not rated down. Original plans for two people to independently assess the quality of the evidence across each health outcome were amended for feasibility reasons. As such, one reviewer evaluated the quality of the evidence and a second person checked the GRADE tables as a quality control measure. GRADE tables are presented in online supplementary tables 2–9.
Statistical analyses were conducted using Review Manager V.5.3 (Cochrane Collaboration, Copenhagen, Denmark). For all dichotomous outcomes, ORs were calculated. Inverse-variance weighting was applied to obtain OR using a random effects model. For continuous outcomes, mean differences between exercise and control groups were calculated. When applicable, change scores were calculated using the generic inverse variance method (Cochrane Collaboration, Copenhagen).28 Significance was set at p<0.05.
A staged approach was used to determine if there was sufficient evidence from high-quality study designs (ie, RCTs) to inform the Guideline, or if lower quality study designs needed to be examined. If meta-analyses of RCTs contained data from fewer than 2000 women, the impact of prenatal exercise on the specific outcome was examined further using observational evidence (first non-randomised interventions, followed by cohort, cross-sectional and case–control studies).
Meta-analyses were performed separately by study design. For RCTs and non-randomised interventions, sensitivity analyses were performed to evaluate whether the effects were different when examining the relationships between exercise-only interventions (including standard care) versus exercise+cointerventions and the outcomes of interest. A priori-determined subgroup analyses were conducted for exercise-only interventions and observational studies when possible. These subgroups included: (1) women diagnosed with diabetes (gestational, type 1 or type 2) compared with women without diabetes; (2) women with prepregnancy overweight or obesity status (mean BMI >25.0 kg/m2) compared with women who were of various BMI (mean BMI <25 kg/m2, which may include some individuals with BMI >25.0 kg/m2); (3) women >35 years of age compared with women <35 years of age; (4) women who were previously inactive compared with those who were previously active (as defined by individual study authors). If a study did not provide sufficient detail to allow for inclusion into the a priori subgroups, then a third group called ‘unspecified’ was created. A priori subgroup analyses were also conducted for exercise-only RCTs to identify whether a specific type of exercise was associated with greater benefit. Due to feasibility, these subgroup analyses were only conducted for ‘critical’ outcomes. Tests for subgroup differences were conducted, with statistical significance set at p≤0.05. Effects within subgroups were only interpreted when statistically significant differences between subgroups were found. The percent of total variability that is attributable to between-study heterogeneity (ie, not to chance) was expressed using the I-squared (I2) statistic. In studies where there were no observed events in the intervention or control group, data were entered into forest plots but were considered ‘not estimable’ and excluded from the pooled analysis as per the recommendation in the Cochrane Handbook.26
In order to identify a clinically meaningful decrease in the outcomes of interest, dose–response meta-regression29–31 was carried out by weighted no-intercept of log OR with a random effects for study, using the metafor32 package in R (V.3.4.1).33 It was determined that an accepted cut-point for a clinically meaningful decrease does not exist in the literature. As such, a reduction of 25% was chosen based on expert opinion. Models did not include an intercept term since the log OR is assumed to be zero when the exercise dose is zero. Restricted cubic splines with knots at the 10th, 50th and 90th percentiles of the explanatory variable34 were used to investigate whether there was evidence for a non-linear relationship. Fitting was performed by maximum likelihood, and non-linearity was assessed using a likelihood ratio test. When the model was statistically significant at p<0.05, the minimum exercise dose to obtain a clinically significant benefit was estimated by the minimum value of the explanatory variable at which the estimated OR was less than 0.75. Linear models were presented unless the fit of the spline was significantly better (p<0.05).
For outcomes where a meta-analysis was not possible, results were presented as a narrative synthesis, structured around each outcome. Within each outcome, results were organised by study design. Unless otherwise specified, studies were not included in meta-analyses if data were reported incompletely (eg, SD, SE or number of cases/controls not provided), if data were adjusted for confounding factors or if the study did not include a non-exercise control group). In studies where data were included in the meta-analysis but additional information was available that could not be meta-analysed (eg, adjusted data), the studies were included in both the meta-analysis and narrative synthesis.
Although the initial search was not limited by language, the Guidelines Steering Committee decided to exclude studies published in languages other than English, Spanish or French for feasibility reasons. A PRISMA diagram of the search results, including reasons for exclusion, is shown in figure 1. A comprehensive list of excluded studies is presented in the online supplementary data. Consistent with the planned staged approach, when there were fewer than 2000 women included in the RCTs, additional study designs were considered.
One hundred and thirteen unique studies (n=52 858 women) from 28 countries met the inclusion criteria. There were 79 RCTs (including 59 exercise-only interventions and 20 exercise+cointerventions), 12 non-RCTs and 22 observational studies. Among the included exercise-only interventions, the frequency of exercise ranged from 1 day to 7 days per week, the duration of exercise ranged from 10 min to 120 min per session, and the types of exercise included walking, swimming, cycling, water gymnastics, resistance training, stretching, yoga or pelvic floor muscle training. Additional details about the studies can be found in the online supplementary (study characteristics and online supplementary table 1). The complete results for preterm rupture of membranes, caesarean section and instrumental delivery are presented below; the results for other outcomes are presented in the online supplementary data.
Quality of evidence
The quality of evidence ranged from ‘very low’ to ‘high’ (see online supplementary tables 2–9). The most common reasons for downgrading the quality of evidence were: (1) serious risk of bias, (2) inconsistency and (3) indirectness of the interventions being assessed. Common sources of bias included poor or unreported compliance to the intervention and inappropriate treatment of missing data when attrition rate was high. No evidence of publication bias was observed among the analyses where it was possible to systematically assess publication bias using funnel plots.
Synthesis of data
Results from meta-regression analyses did not identify a dose–response relationship between frequency, intensity, duration or volume of exercise and any labour and delivery outcomes (see online supplementary figures 56-62).
Preterm rupture of membranes
There was ‘very low’ quality evidence from four RCTs (n=337 women) indicating that prenatal exercise did not affect the odds of preterm rupture of membranes (OR 1.01, 95% CI 0.38 to 2.68, I2=21%; figure 2).35–38 The quality of the evidence was downgraded from ‘high’ to ‘very low’ because of serious risk of bias, serious indirectness of the intervention and serious imprecision.
The pooled estimate for the exercise-only interventions was not significantly different than the pooled estimate for the exercise+cointervention subgroups (p=0.79). Both exercise-only interventions (two RCTs, n=198 women)37 38 and exercise+cointerventions (two RCTs, n=139 women)35 36 did not affect the odds of preterm rupture of membranes (figure 2).
It was not possible to conduct tests for subgroup differences within exercise-only interventions because there was only one exercise-only intervention reporting estimable results (online supplementary figures 1 and 2).
Other study designs
Findings from two non-randomised interventions39 40 and five cohort studies41–45 were consistent with the findings from the RCTs. Specifically, there was ‘very low’ quality evidence (downgraded due to serious risk of bias, serious indirectness of the intervention and serious imprecision) from two non-randomised exercise+cointerventions (n=394 women) showing no effect of prenatal exercise on the odds of preterm rupture of membranes (OR 0.54, 95% CI 0.24 to 1.21, I2=0%; online supplementary figure 3).39 40
Similarly, there was ‘very low’ quality evidence (downgraded due to serious risk of bias and serious imprecision) from five cohort studies (n=1767) indicating no effect of prenatal exercise on the odds of preterm rupture of membranes (pooled estimate based on four studies, n=1577; OR 1.13, 95% CI 0.79 to 1.62, I2=0%; online supplementary figure 4).41–43 45 The one cohort study (n=190) that could not be included in the meta-analysis found no association between accumulated weekly minutes spent exercising and odds of preterm rupture of membranes44 (online supplementary table 1).
There was ‘low’ quality evidence from 67 RCTs (n=18 435 women) indicating decreased odds of caesarean section (pooled estimate based on 66 RCTs, n=15 888; OR 0.87, 95% CI 0.80 to 0.96, I2=16%; figure 3).36–38 46–108 The quality of the evidence was downgraded from ‘high’ to ‘low’ because of serious risk of bias and serious indirectness of the intervention. The one superiority exercise-only intervention that could not be included in the meta-analysis (no non-exercise control group) reported similar rates of caesarean section between the walking group (n=1255 women) and the pelvic rocking exercise group (n=1292) (online supplementary table 1).109
The pooled estimate for the exercise-only interventions were not significantly different than the pooled estimate for the exercise+cointervention (p=0.64). However, exercise+cointerventions reduced the odds of caesarean section (21 RCTs, n=7888 women; OR 0.87, 95% CI 0.79 to 0.97, I2=0%; figure 3).36 69 89–103 105–108 There was no statistically significant difference for those participating in exercise-only interventions compared with no exercise (figure 3).
The tests for subgroup differences performed for exercise-only interventions were not significant (online supplementary figures 7, 8 and 9).
Overall, there was ‘low’ quality evidence from 26 RCTs (n=9650 women) regarding the association between prenatal exercise and instrumental delivery.35 47–51 55–57 59 65 74 77 80 82–87 92 97 99 105 109 110 The quality of evidence was downgraded from ‘high’ to ‘low’ because of serious risk of bias and serious indirectness of the interventions. Overall, prenatal exercise did not affect the odds of instrumental delivery (pooled estimate based on 25 RCTs, n=7103; OR 0.90, 95% CI 0.78 to 1.03, I2=0%; figure 4.35 47–51 55–57 59 65 74 77 80 82–87 92 97 99 105">–87 92 97 99 105 110 One exercise-only superiority RCT could not be included in the meta-analysis because it did not have a non-exercise control group reported similar rates of instrumental delivery between the walking group (n=1255 women) and the pelvic rocking exercise group (n=1292 women) (online supplementary table 1).109
The pooled estimate for the exercise-only interventions was significantly different than the pooled estimate for the exercise+cointervention subgroups (p=0.009). There was ‘moderate’ quality evidence (downgraded due to serious risk of bias) indicating that exercise-only interventions (20 RCTs, n=3819 women) reduced the odds of instrumental delivery (OR 0.76, 95% CI 0.63 to 0.92, I2=0%; figure 4 .47–51 55–57 59 65 74 77–57 59 65 74 77 80 82–87 110 Exercise+cointerventions did not affect the odds of instrumental delivery (5 RCTs, n=3284 women; OR 1.10, 95% CI 0.90 to 1.36, I2=0%;
The tests for subgroup differences performed for exercise-only interventions were not statistically significant (online supplementary figures 13 and 14).
There were no significant associations between prenatal exercise and any remaining outcomes (caesarean section/instrumental delivery, induction of labour, length of labour, vaginal tears, fatigue, injury, musculoskeletal trauma, maternal harms [author defined] and diastasis recti) for either the complete sample or subgroups (see online supplementary for additional details).
Our systematic review and meta-analysis of the impact of prenatal exercise on labour and delivery complications, and maternal harms, found ‘moderate’ quality evidence from exercise-only RCTs indicating prenatal exercise was associated with a 24% reduction in the odds of instrumental delivery. Prenatal exercise was not associated with preterm/prelabour rupture of membranes, caesarean section, induction of labour, length of labour, vaginal tears, fatigue, injury (author defined), musculoskeletal trauma, maternal harms (author defined) or diastasis recti. Results from meta-regression did not identify a dose–response relationship between frequency, intensity, duration or volume of exercise and labour and delivery outcomes.
Habitual prenatal exercise decreases the risk of complications during labour.111 Although it is beyond the scope of this review to identify the underlying cause of the reduced instrumental delivery, macrosomia has been identified as a risk factor for the use of forceps or vacuum extraction.112 Previous work has identified that prenatal exercise reduces the odds of fetal macrosomia by 31%,113 and as a result, may reduce the risk for instrumental delivery. Furthermore, a potential role of excessive gestational weight gain on risk of operative delivery has been suggested, even in women with a healthy prepregnancy BMI.114 We previously showed that prenatal exercise reduces the odds of excessive gestational weight gain by 32%,115 which may indirectly reduce the odds of instrumental delivery.
Women with assisted delivery and caesarean section face an increased risk of maternal/fetal morbidity and mortality116 and an increased risk of being rehospitalised.117 Women who experience spontaneous vaginal birth with little damage to the perineum have fewer complications postpartum, while assisted vaginal delivery may result in higher incidence of short-term and long-term morbidity.118 The reduced odds of instrumental delivery with prenatal exercise may reduce these complications. The finding that prenatal exercise was not associated with other labour and delivery outcomes should reassure pregnant women and healthcare providers that prenatal exercise does not increase the risk of musculoskeletal injury or premature delivery.
Strengths of the review included the rigorous methodological standard (GRADE) used to guide the systematic review process, examination of grey literature and assessing articles in English, French and Spanish. Twenty-eight countries from five continents were represented. Quality of evidence from the RCTs was rated down mainly because of risk of bias and indirectness of the interventions. Risk of bias included performance bias where studies were downgraded due to issues related to compliance. Compliance with the intervention is a critical factor in determining whether an intervention is effective. In studies where compliance was measured, reporting of studies was inconsistent, and this made it difficult to determine intervention effectiveness. We noted a lack of studies examining the impact of prenatal exercise on labour and delivery outcomes in women with obesity, gestational diabetes mellitus or women who were over 35 years.
In conclusion, we identified that prenatal exercise reduced the risk of instrumental delivery in the general obstetrical population by 24%. This substantial effect, combined with other findings of our systematic reviews,13 contributes to a strong case for a net beneficial role of exercise during pregnancy.
The authors wish to acknowledge Mary Duggan from the Canadian Society for Exercise Physiology who is the primary knowledge user for the Canadian Institute of Health Research Knowledge Synthesis Grant. The authors also wish to thank Anne Courbalay and Baily Shandro for their assistance with the systematic review, and Meghan Sebastianski from the Alberta SPOR SUPPORT Unit Knowledge Translation Platform, University of Alberta, for her assistance with the meta-analysis.
Contributors MHD, S-MR, MFM, GAD and KBA contributed to the conception of the study. MHD, S-MR, MFM, GAD, KBA, AJG, NB, VJP, CEG, LGS and RB contributed to the design of the study and development of the search strategy. LGS conducted the systematic search. FS, CY, RS, TSN, LR, MJ, MN, AW and A-AM completed the acquisition of data. MHD, NB and MN performed the data analysis. All authors assisted with the interpretation. MHD, S-MR, FS and CY were the principal writers of the manuscript. All authors contributed to the drafting and revision of the final article. All authors approved the final submitted version of the manuscript.
Funding Canadian Institute of Health Research Knowledge Synthesis Grant (grant number: 140995). MHD is funded by an Advancing Women’s Heart Health Initiative New Investigator Award supported by Health Canada and the Heart and Stroke Foundation of Canada (grant number: RES0033140). RS is funded by a Canadian Institutes for Health Research Doctoral Research Award (grant number: GSD- 146252). AAM is funded by a Fonds de Recherche du Québec – Santé Doctoral Research Award (grant number: 34399).
Competing interests None declared.
Patient consent Not required.
Provenance and peer review Not commissioned; externally peer reviewed.