Growth Velocity and Sonographic Estimation of Birthweight Among Low-Risk Pregnancies.

To examine whether addition of fetal growth velocities, based on serial scans, compared to estimated fetal weight (EFW) alone, improves prediction accuracy of birthweight (BW). From the prospective NICHD Fetal Growth Studies-Singletons (2009-2013) that recruited women at low-risk for aberrant fetal growth, we included 2,397 participants with two to five ultrasounds between 15-41 weeks. Fetal growth velocity (V) was calculated between successive visits. Linear regression estimated relationship between EFW and BW: Non-V model, absent all growth velocities, included EFW at visit 5, interval from visit 5 to delivery, their cubic polynomials, and delivery gestational age (GA); All-V model added all available velocities between research visits (i.e., V2+V3+V4+V5) to the Non-V model; Single-V model added only the velocity between visit 4 and 5. Non-V performed the worst, with the highest mean absolute error of 197 g and lowest R2, 0.63. The two best performing models were All-V and Single-V, with the lowest mean absolute error (192 g for both), highest R2 of 0.65 (for both), and greatest proportion of predicted BWs within 10% of actual BW (84.7% for both). Integrating fetal growth velocities into BW estimating formulas improved BW prediction accuracy which has potential to guide clinical intervention decisions that rely on EFW.