Determination of the Latency Period Between Weekly Gestational Weight Gain and Fetal Growth

BACKGROUND: Gestational weight gain (GWG) is associated with fetal growth. However, prior studies have assumed specific timing and latency between GWG and fetal growth. OBJECTIVES: We aimed to identify the latency period between the cumulative GWG rate and fetal growth and assess whether accounting for it changes their association. METHODS: We analysed data from the NICHD Fetal Growth Studies-Singletons (N = 2445) and NICHD Fetal 3D Study (n = 1946). Maternal cumulative GWG rate was the exposure; fetal growth outcomes were estimated fetal weight (EFW) from 2D ultrasound and fractional arm volume (AVol) from 3D. Weekly cumulative GWG rate and fetal growth trajectories were estimated. Two procedures were used to select latency period: one approach identifies the lag with the largest association, and the other the best model fit. Models were adjusted for sociodemographic, clinical, and lifestyle covariates. RESULTS: (95% CI 6.6, 7.8) in AVol at week 40. Results were similar under the 8-week lag specification, with overlapping confidence intervals. CONCLUSIONS: Using two common latency selection procedures, we identified a 7-8 week latency period between GWG and subsequent fetal growth, with consistent findings across 2D and 3D fetal growth parameters. These findings highlight the importance of identifying relevant latency periods between GWG and its relationship with fetal growth and the need for improved statistical methods to address the limitations of current latency selection procedures.