Classifying Gestational Weight Gain Trajectories Using the SITAR Growth Model

Area of Science:

• Obstetrics and Gynecology
• Biostatistics
• Maternal-Fetal Medicine

Background:

• Gestational weight gain (GWG) is typically measured by total amount, but the pattern of gain is crucial for maternal and fetal health outcomes.
• The Super Imposition by Translation And Rotation (SITAR) model, known for its biologically interpretable parameters, has successfully modeled childhood growth trajectories.
• Applying the SITAR model to GWG trajectories offers a novel approach to understanding pregnancy weight dynamics.

Purpose of the Study:

• To assess the feasibility of applying the SITAR model to describe gestational weight gain (GWG) trajectories.
• To characterize GWG patterns, including amount, timing, and acceleration, across different pre-pregnancy body mass index (BMI) categories.

Main Methods:

• A cohort of 3470 women (normal-weight, overweight, obese) was analyzed using serial prenatal weight measurements.
• The SITAR model, a non-linear mixed-effects model, was applied to GWG data stratified by pre-pregnancy BMI.
• Model complexity was varied, with the best-fitting model selected to represent GWG patterns for each BMI group.

Main Results:

• Reduced SITAR models successfully converged after modifications, explaining 95%-97% of the variation in GWG trajectories.
• Peak rates of weight gain were observed between 20-22 weeks gestation.
• Peak GWG rates were higher in normal-weight (0.59 kg/week) and overweight (0.57 kg/week) women compared to obese women (0.46 kg/week).

Conclusions:

• The SITAR model, with necessary adjustments, is a feasible and effective tool for characterizing gestational weight gain patterns.
• Understanding these patterns can provide deeper insights into pregnancy health and outcomes across diverse BMI groups.