Assessment of fetal growth trajectories between the second and third trimesters using INTERGROWTH-21st estimated fetal weight Z-scores

OBJECTIVES: To identify fetal growth trajectories between the second and third trimesters using changes in INTERGROWTH-21st estimated fetal weight (EFW) Z-scores and to evaluate their relationship with fetal size categories in uncomplicated singleton pregnancies. MATERIAL AND METHODS: This retrospective cohort study included 615 uncomplicated singleton pregnancies with routine ultrasound examinations performed in the second and third trimesters. EFW was calculated from standard biometric parameters and converted into gestational age-specific Z-scores according to the INTERGROWTH-21st standards. The change in EFW Z-score between the two examinations (ΔZ_EFW) was used to classify fetal growth trajectories as declining, stable, or increasing. Group comparisons were performed using one-way analysis of variance and Student's t-tests. RESULTS: A declining trajectory was identified in 336 fetuses (54.6%), a stable trajectory in 228 (37.1%), and an increasing trajectory in 51 (8.3%). Mean EFW Z-scores decreased significantly between the second and third trimesters in the overall cohort (0.80 ± 0.95 vs 0.20 ± 1.02; p < 0.001). Third-trimester EFW Z-scores differed significantly between trajectory groups (p < 0.001). SGA newborns were observed predominantly in the declining trajectory, whereas stable and increasing trajectories were mainly associated with AGA and LGA outcomes. CONCLUSIONS: Assessment of fetal growth trajectories based on changes in EFW Z-scores between two routine ultrasound examinations may complement conventional fetal growth assessment by identifying fetuses with slowing growth despite maintaining an estimated fetal weight within the normal range. This simple approach may provide additional clinically relevant information beyond a single cross-sectional fetal biometry measurement.