2. Individual Patient Data (IPD) meta-analysis
This phase of the research aims to establish an international individual participant data (IPD) collaboration to share data on early pregnancy adiposity and pregnancy outcomes. Data obtained from this phase will be used as an external validation dataset. We will use IPD meta-analysis methods to determine whether the prediction model(s) developed in phase 1 (SHAPES cohort study) produce similar findings when applied to external populations.
This phase has built on our previous systematic reviews which identified existing published studies that measured early pregnancy adiposity (alternative to BMI) <20 weeks gestation and reported associations with adverse maternal and infant pregnancy outcomes. We updated these searches to identify any studies which collected early pregnancy adiposity measures and pregnancy outcomes, even if they did not report associations between these variables. This stage involved rescreening the studies excluded from the previous reviews as well as searching for pregnancy cohort studies which may have collected, but not published, these data. The protocol for this stage has been registered on PROSPERO.
Authors of eligible studies have been invited to join an international IPD collaboration. We have established data sharing and co-authorship agreements with the authors who agree to collaborate in the IPD study. The IPD has been obtained in an anonymised format and stored in a secure data repository.
We will externally validate the risk prediction model(s) using calibration and discrimination analyses. Calibration will examine the agreement between the probability of developing the outcome as estimated by the model, and the observed outcome frequencies (assessed with plots). Discrimination analysis will examine the ability of the model to distinguish between individuals who develop the outcomes or not. This will be assessed using the c-index (area under the receiver operating characteristic curve).
We began contacting authors of identified eligible studies from May 2022. We are currently in the process of analysing this data.
An update on progress: June 2025
We identified 93 published and unpublished sources of maternal adiposity and pregnancy outcome data. Authors were invited to join the SHAPES-IPD Collaborative Group, resulting in 20 shared IPD datasets (n=15 countries, n=15,568 pregnancies). One author agreed to replicate the SHAPES-IPD statistical analysis plan (SAP) for stage 1 of the IPD meta-analysis and share their aggregate data for inclusion in the stage 2 meta-analysis.
