Objective To synthesise the evidence on the overall and differential effects of interventions
based on diet and physical activity during pregnancy, primarily on gestational weight
gain and maternal and offspring composite outcomes, according to women's body mass
index, age, parity, ethnicity, and pre-existing medical condition; and secondarily
on individual complications.Design Systematic review and meta-analysis of individual
participant data (IPD). Data sources Major electronic databases from inception to
February 2017 without language restrictions.Eligibility criteria for selecting studies Randomised
trials on diet and physical activity based interventions in pregnancy.Data synthesis Statistical
models accounted for clustering of participants within trials and heterogeneity across
trials leading to summary mean differences or odds ratios with 95% confidence intervals
for the effects overall, and in subgroups (interactions).Results IPD were obtained
from 36 randomised trials (12 526 women). Less weight gain occurred in the intervention
group than control group (mean difference -0.70 kg, 95% confidence interval -0.92
to -0.48 kg, I2=14.1%; 33 studies, 9320 women). Although summary effect estimates
favoured the intervention, the reductions in maternal (odds ratio 0.90, 95% confidence
interval 0.79 to 1.03, I2=26.7%; 24 studies, 8852 women) and offspring (0.94, 0.83
to 1.08, I2=0%; 18 studies, 7981 women) composite outcomes were not statistically
significant. No evidence was found of differential intervention effects across subgroups,
for either gestational weight gain or composite outcomes. There was strong evidence
that interventions reduced the odds of caesarean section (0.91, 0.83 to 0.99, I2=0%;
32 studies, 11 410 women), but not for other individual complications in IPD meta-analysis.
When IPD were supplemented with study level data from studies that did not provide
IPD, the overall effect was similar, with stronger evidence of benefit for gestational
diabetes (0.76, 0.65 to 0.89, I2=36.8%; 59 studies, 16 885 women).Conclusion Diet
and physical activity based interventions during pregnancy reduce gestational weight
gain and lower the odds of caesarean section. There is no evidence that effects differ
across subgroups of women.