Modelling gestational weight gain trajectories and risk of adverse birth outcomes using super imposition by translation and rotation: findings from two Brazilian cohort studies

Background Gestational weight gain (GWG) is a key determinant of maternal and neonatal health, yet there are no clear recommendations for tracking GWG trajectories, beyond total amount, in routine care. We aimed to characterise GWG trajectories in terms of both amount and velocity and examine their associations with adverse neonatal outcomes in two Brazilian cohorts, using INTERGROWTH-21st (IG-21st) centiles. Methods We analysed 3770 pregnant women in two population-based cohorts in São Paulo state, Brazil: Jundiaí (n = 965; 1997–2000; median age 24 years [IQR 20–29]; 21% non-White) and Araraquara (n = 2805; 2017–2024; median age 27 years [IQR 22–32]; 54% non-White). GWG trajectories were modelled using the Super Imposition by Translation and Rotation (SITAR) method. Predicted GWG amount and velocity were classified against IG-21st 25th and 75th centiles for women with normal weight. Associations with low birthweight (LBW), macrosomia, preterm birth (PTB), and 5-min Apgar score <7 were estimated using multivariable Poisson regression with robust variance estimation. Findings SITAR explained 85.6% of GWG variance in Jundiaí and 84.0% in Araraquara. GWG below the 25th centile was associated with LBW (RR 2.14; 95% CI 1.47–3.11) and PTB (RR 1.95; 95% CI 1.20–3.17); above the 75th centile, with macrosomia (RR 2.58; 95% CI 1.40–4.77). GWG velocity above the 75th centile was strongly associated with macrosomia (RR 3.31; 1.58–6.92). Interpretation SITAR provided a parsimonious description of GWG trajectories and identified clinically relevant deviations in amount and velocity. IG-21st 25th and 75th centiles offer risk stratification identifying those most at risk of poor neonatal outcomes. Funding São Paulo Research Foundation (FAPESP).