Gestational weight gain (GWG) is an important indicator of maternal nutrition to be monitored during pregnancy. However, there is no evidence-based tool that can be used to monitor it across all geographic locations and pre-pregnancy body mass index (BMI) categories. The WHO is undertaking a project to develop GWG charts by pre-pregnancy BMI category, and to identify GWG ranges associated with the lowest risks of adverse maternal and infant outcomes. This protocol describes all the steps that will be used to accomplish the development of these GWG charts.

This project will involve the analysis of individual participant data (researcher-collected or administrative). To identify eligible datasets with GWG data, a literature review will be conducted and a global call for data will be launched by the WHO. Eligible individual datasets obtained from multiple sources will be harmonised into a pooled database. The database will undergo steps of cleaning, data quality assessment and application of individual-level inclusion criteria. Heterogeneity of maternal weight and GWG will be assessed to verify the possibility of combining datasets from multiple sources and regions into a single database. Generalized Additive Models for Location, Scale and Shape will be applied for the construction of the centile curves. Diagnostic measures, internal and external validation procedures will also be performed.

This project will include an analysis of existing study de-identified data. To be included in the pooled database, each included study should have received ethics approvals from relevant committees. Manuscripts will be submitted to open-access journals and a WHO document will be published, including the GWG charts and cut-offs for application in antenatal care.