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Background: Diet- and physical activity-based interventions in pregnancy have the potential to alter maternal and child outcomes. Objectives: To assess whether or not the effects of diet and lifestyle interventions vary in subgroups of women, based on maternal body mass index (BMI), age, parity, Caucasian ethnicity and underlying medical condition(s), by undertaking an individual patient data (IPD) meta-analysis. We also evaluated the association of gestational weight gain (GWG) with adverse pregnancy outcomes and assessed the cost-effectiveness of the interventions. Data sources: MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Database of Abstracts of Reviews of Effects and Health Technology Assessment database were searched from October 2013 to March 2015 (to update a previous search). Review methods: Researchers from the International Weight Management in Pregnancy Collaborative Network shared the primary data. For each intervention type and outcome, we performed a two-step IPD random-effects meta-analysis, for all women (except underweight) combined and for each subgroup of interest, to obtain summary estimates of effects and 95% confidence intervals (CIs), and synthesised the differences in effects between subgroups. In the first stage, we fitted a linear regression adjusted for baseline (for continuous outcomes) or a logistic regression model (for binary outcomes) in each study separately; estimates were combined across studies using random-effects meta-analysis models. We quantified the relationship between weight gain and complications, and undertook a decision-analytic model-based economic evaluation to assess the cost-effectiveness of the interventions. Results: Diet and lifestyle interventions reduced GWG by an average of 0.70 kg (95% CI –0.92 to –0.48 kg; 33 studies, 9320 women). The effects on composite maternal outcome [summary odds ratio (OR) 0.90, 95% CI 0.79 to 1.03; 24 studies, 8852 women] and composite fetal/neonatal outcome (summary 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 GWG, and composite maternal and fetal outcomes. Lifestyle interventions reduce Caesarean sections (OR 0.91, 95% CI 0.83 to 0.99), but not other individual maternal outcomes such as gestational diabetes mellitus (OR 0.89, 95% CI 0.72 to 1.10), pre-eclampsia or pregnancy-induced hypertension (OR 0.95, 95% CI 0.78 to 1.16) and preterm birth (OR 0.94, 95% CI 0.78 to 1.13). There was no significant effect on fetal outcomes. The interventions were not cost-effective. GWG, including adherence to the Institute of Medicine-recommended targets, was not associated with a reduction in complications. Predictors of GWG were maternal age (summary estimate –0.10 kg, 95% CI –0.14 to –0.06 kg) and multiparity (summary estimate –0.73 kg, 95% CI –1.24 to –0.23 kg). Limitations: The findings were limited by the lack of standardisation in the components of intervention, residual heterogeneity in effects across studies for most analyses and the unavailability of IPD in some studies. Conclusion: Diet and lifestyle interventions in pregnancy are clinically effective in reducing GWG irrespective of risk factors, with no effects on composite maternal and fetal outcomes. Future work: The differential effects of lifestyle interventions on individual pregnancy outcomes need evaluation. Study registration: This study is registered as PROSPERO CRD42013003804. Funding: The National Institute for Health Research Health Technology Assessment programme.

Objective: To examine the representativeness of participants attending a lifestyle intervention study addressing obese pregnant women. Methods: Retrospective comparison of baseline data, attendance to oral glucose tolerance test (OGTT) during pregnancy, and pregnancy outcome in eligible women stratified according to study participation. Of 750 eligible women with a self-reported BMI > 30 kg/m2, and a live singleton pregnancy, 510 were eligible for inclusion and 425 were randomized to either active intervention (n= 284) or to standard obstetric care (n= 141) including two standard OGTT. The 85 women who declined participation or were excluded due to competing diseases and 240 women who did not respond to the initial invitation received the same standard care. Results: The randomized women had similar BMI but a lower parity and age, and were more frequently non-smokers, born in Denmark and married or cohabitating with their partner than the non-participants. Women participating in the trial had a higher compliance to the second OGTT compared to non-participants, also after correcting for age and nationality. There was no difference in pregnancy outcome, i.e., fetal weight and length, gestational age as well as mode of delivery. Conclusion: Women declining participation in a randomized lifestyle intervention study in pregnancy have characteristics indicating they are those who might benefit the most from lifestyle intervention.