The value of fetal growth trajectory during pregnancy in predicting small for gestational age neonates at term

The predictive value of trajectory identified by group-based trajectory modeling (GBTM) has been discussed but its value in predicting small for gestational age (SGA) neonates is still unclear. This study aims to describe the trajectory of fetal growth of estimated fetal weight (EFW) during pregnancy and compare its performance to growth velocity of EFW and EFW z-scores at each scan in predicting SGA neonates at term.

The growth trajectory for EFW obtained from ultrasound scan at around 23-24, 31-32, 37-39 weeks of gestation of 1699 women from Shenzhen Birth Cohort Study was identified using GBTM. The area under receiver operating characteristics curve (AUC), Brier scores and Decision curve analysis (DCA) was used to evaluate the discrimination, calibration performance and clinical usefulness of EFW growth trajectory, EFW growth velocity between each stage and EFW z-scores at each scan.

Four trajectory groups of EFW which described as "very low-stable", "low-stable", "average-stable", "rising-falling" were identified. The growth trajectory performed better in discrimination and calibration than growth velocity, with AUC of 0.76 (95%CI: 0.73-0.80) and Brier score of 0.067 in predicting SGA neonates at term. When compared to the EFW z-scores, growth trajectory performed better than EFW z-scores of 23-24 weeks (AUC = 0.72, 95%CI: 0.68-0.76, Brier score = 0.073), but not as well as EFW z-scores of 37-39 weeks of gestation (AUC = 0.88, 95%CI: 0.86-0.91, Brier score = 0.060).

EFW z-scores of 37-39 weeks of gestation outperformed in predicting SGA neonates at term than growth trajectory and velocity. Growth trajectory has better potential for serial ultrasound examinations to describe the process of fetal growth and to predict SGA neonates at term than fetal growth velocity.