OBJECTIVE: To assess if the effects of diet and physical activity basedinterventions vary in subgroups women based on body mass index(BMI) at booking, age, parity, ethnicity and underlying medicalconditions. STUDY DESIGN: Individual Participant Data meta-analysis of randomised trials (RCTs) with diet and physical activity in pregnancy. Theeffect of interventions was evaluated on gestational weight gain,composite maternal and fetal/neonatal outcomes. The maternalcomposite comprised of gestational diabetes mellitus (GDM), preeclampsia or pregnancy-induced hypertension (PE or PIH), pretermbirth and caesarean section. The composite fetal /neonatal outcome included intrauterine death, small for gestational age, large for gestational age and admission to Neonatal Intensive Care Unit. The summary estimates of effects and 95% confidence intervals wereobtained through a two-step IPD random-effects meta-analysis. The methodological quality of identified studies was assessed using Cochrane risk of bias. RESULTS: Thirty-six RCTs (12,434 women) with diet and physical activity-based interventions contributed to this IPD meta-analysis. The interventions reduced gestational weight gain by an average of 0.70 kg (95% CI: -0.92 to -0.48, 33 studies, 9320 women). The effects on composite maternal outcome (OR 0.90, 95% CI: 0.79 to 1.03, 24 studies, 8852 women) and composite fetal / neonatal outcome (OR 0.94, 95% CI: 0.83 to 1.08, 18 studies, 7981 women) were not significant. The effect did not vary with baseline BMI, age,ethnicity, parity or underlying medical conditions for gestational weight gain, and composite maternal and fetal outcomes. CONCLUSION: Diet and lifestyle interventions should be offered to all pregnant mothers, irrespective of risk factors, to reduce excess gestational weight gain.