Antenatal physical activity interventions not tied to improved pregnancy outcomes: Study
Multiple systematic reviews and meta-analyses have considered the question of whether antenatal physical activity, compared with no such intervention, can improve pregnancy outcomes. Reported benefits of a physical activity intervention include a reduction in gestational weight gain and the risk of adverse pregnancy outcomes such as preeclampsia and gestational diabetes mellitus (GDM). Such reviews have informed national and international pregnancy care guidelines, with recommendations that pregnant women engage in regular physical activity in pregnancy.
The principle of systematic reviews and meta-analyses is to synthesise the available evidence, generating an aggregate effect estimate from multiple studies. As part of this process, assessment of individual trial quality is generally undertaken, commonly utilising the Cochrane Risk of Bias tool 2.0, to assess risk of bias across multiple domains, including the impact of missing outcome data. A central tenet of a rigorous randomised trial is the inclusion of outcome data from all participants recruited and randomised in an intention-to-treat (ITT) analysis. Failure to undertake an ITT analysis introduces bias reflecting not only the extent of missing outcomes but also the degree of “missingness”, which can be related to the nature of the intervention. This is of particular relevance when considering physical activity interventions, where the underlying characteristics and clinical outcomes of those who comply are likely different from those who do not. Furthermore, exclusion of participants who are non-compliant with an intervention limits the generalisability of the findings into clinical practice. The aim was to conduct a methodologically rigorous systematic review to evaluate physical activity interventions in pregnancy on clinical pregnancy outcomes and to assess the impact of including studies at increasing risk of bias on the validity of recommendations for clinical practice guidelines.
This systematic review considered all randomised trials that evaluated the effect of an antenatal physical activity intervention alone (i.e., the intervention did not include dietary or behavioural components). Systematic search of PubMed, PubMed Central, Ovid Medline, Embase, Cochrane Central Register of Controlled Trials, and CINAHL from inception to 14 December 2023. Trial quality was assessed using the Cochrane Risk of Bias tool. Independent of this, studies were grouped based on degree of deviation from the intention to treat principle. Sequential meta-analysis was performed in which greater degrees of potential bias were allowed. Between intervention group comparisons used, relative risks or mean differences with 95% confidence intervals for dichotomous outcomes and continuous outcomes, respectively.
Overall, the quality of trial reporting was low. Only 5 trials (12.5%) were performed and analysed in keeping with the intention to treat principle. When considering only those trials performed rigorously, there was no evidence that antenatal physical activity improves pregnancy outcomes or limits gestational weight gain (WMD −0.60kg; 95% CI −2.17, 0.98 WMD −0.60kg; 95% CI −2.17, 0.98).
Authors found no evidence that antenatal physical activity is associated with improved pregnancy outcomes or reduced gestational weight gain when considering only trials considered to have no or negligible risk of bias. The effect of including trials with increasing potential for bias shifted the estimates of effect further from the null while simultaneously introducing greater heterogeneity.
Study findings are in contrast with those of published systematic reviews and meta-analyses that have been used to inform national and international guidelines for pregnancy care. In particular, recently published systematic reviews and meta-analyses have reported that antenatal physical activity interventions are associated with a reduction in gestational diabetes, hypertensive disorders of pregnancy, and gestational weight gain. These aggregate data meta-analyses included all trials, irrespective of individual trial risk of bias or rigour.
Authors have demonstrated in review that a small minority of randomised trials have been conducted in a methodologically rigorous way, the majority of trials having substantial risk of bias, particularly in relation to performing an ITT analysis. When considering only trials at no or negligible risk of bias, there is no effect of antenatal physical activity interventions on gestational weight gain or pregnancy and birth outcomes for women and their infants. In contrast, the inclusion of trials with significant methodological flaws results in misleading findings of benefit. Furthermore, almost half of the trials they identified recruited fewer than 100 women. It is well known that smaller studies often show different, commonly larger, treatment effects than those reported by larger randomised trials. Smaller studies, particularly those with fewer than 100 participants, have been shown to inappropriately skew aggregate data meta-analysis results towards beneficial effects. This has implications for evidence-based clinical practice guidelines that rely on systematic reviews and meta-analyses suffering from artificially inflated effect estimate.
Study findings cast doubt on the validity of national and international clinical practice guidelines recommending antenatal physical activity for improvement of pregnancy outcomes. A rigorous assessment of trial quality is required prior to incorporation of evidence synthesis into such clinical practice guidelines, as study found a significant proportion of included trials were of poor quality and biased aggregate estimates of effect.
Source: Amanda J. Poprzeczny, Andrea R. Deussen, Megan Mitchell; BJOG: An International Journal of Obstetrics & Gynaecology, 2025; 0:1–15 https://doi.org/10.1111/1471-0528.18084
