Investigating discrepancies in findings between rigorous randomized trials and meta-analyses evaluating pregnancy interventions to limit gestational weight gain

Introduction: Robust randomized trials consistently demonstrate little impact from diet and physical activity interventions on gestational weight gain (GWG) and clinical outcomes, although meta-analyses report some benefit. Our aim was to evaluate the effect of trial quality on treatment effect estimates and review conclusions. Methods: We conducted a systematic review of dietary and/or physical activity interventions for pregnant women with a body mass index ≥18.5 kg/m². We assessed studies for risk of bias and methodological features impacting reliability. Outcomes included GWG; gestational diabetes mellitus (GDM); pre-eclampsia; caesarean birth; and birth weight measures. For each outcome, a sequence of meta-analyses was performed based on intervention group and level of potential bias in the effect estimate. Results: We identified 128 eligible studies. The most robust estimate from a combined diet and physical activity behavioral intervention, with only studies at negligible risk of bias, was a difference in GWG of 1.10 kg (95% CI −1.62 to −0.58; 17,755 women). There was no evidence of an effect on any clinical outcomes. Conclusions: Our findings highlight discrepancies produced by the indiscriminate inclusion of studies with methodological flaws in previous systematic reviews. Regular weighing of pregnant women is futile in the absence of clinical benefit.