Estimated fetal weight or gestational age: which is crucial for fetal cardiac evaluation?

Fetal cardiac output is typically assessed using gestational age (GA) or estimated fetal weight (EFW), but the optimal reference remains unclear due to limited validation.

We retrospectively analyzed prospectively collected data from singleton fetuses at 27 + 2 to 29 + 6 weeks of gestation. Subjects included those with small for gestational age (SGA; EFW <10th percentile), large for gestational age (LGA; EFW > 90th percentile), and appropriate for gestational age (AGA), all without structural abnormalities. Associations between fetal cardiac output and both GA and EFW were evaluated using generalized additive models.

Among 443 fetuses with EFWs ranging from 873 to 1631 g, GA showed no significant association with any cardiac parameter (p ≥ 0.282). In contrast, EFW demonstrated significant and largely linear associations with all parameters (p < 0.001, F ≥ 16.7), consistent across GA and EFW ranges. Cardiac parameter distributions by EFW were similar across AGA, SGA, and LGA groups.

EFW showed stronger and more consistent correlations with fetal cardiac parameters than GA, supporting its use as a more reliable reference for fetal cardiac evaluation across different growth statuses.

Fetal cardiac output is typically assessed using reference ranges based on either gestational age (GA) or estimated fetal weight (EFW), both derived from appropriate for gestational age (AGA) fetuses. We showed that EFW is superior to GA for fetal cardiac evaluation. Including non-AGA fetuses confirmed they can be assessed similarly to AGA fetuses. The new EFW-based reference ranges offer a uniform standard, enabling more definitive assessments across varied fetal growth.