(477) Local growth curves overestimate fetal size and may miss pathologic growth restriction

Objective:
Population-based fetal growth curves are expected to improve the detection of pathologic fetal growth restriction (FGR). We compared a local curve (Spiegel‑Yagel, SY) and a universal curve (Hadlock, HL) to evaluate differences in overestimation rates and placental lesion prevalence among small‑for‑gestational‑age (SGA) neonates in a retrospective cohort study.

Study Design:
We retrospectively analyzed 346 singleton pregnancies (2016–2024) with birthweight (BW) < 10th percentile. Group 1: BW < 3rd percentile (n=243); Group 2: BW 3–10th percentile (n=103). Estimated fetal weight (EFW) percentiles were calculated using SY and HL curves. Overestimation was defined as EFW 3–10% despite BW < 3% or EFW >10% despite BW 3–10%. Placental pathology was reviewed per Amsterdam Consensus (2016) and classified as:
• Maternal vascular malperfusion (MVM): distal villous hypoplasia, accelerated villous maturation, decidual arteriopathy, infarction, syncytial knots, villous agglutination.
• Fetal vascular malperfusion (FVM): avascular villi, stromal‑vascular karyorrhexis, thrombosis, villous mineralization.
Lesion prevalence was compared between overestimated and correctly classified SGA cases using chi‑square analysis.

Results:
SY overestimated fetal size more often than HL, especially in BW 3–10% (46.6% vs 21.4%, p=0.006). In BW < 3%, rates were 35.8% (SY) vs 28.4% (HL). Placental lesions were frequent in overestimated cases, with MVM in 52–64% and FVM in 28–42%, meaning over half of fetuses classified as non‑SGA still had placental pathology. No significant difference in lesion prevalence was observed between overestimated and correctly classified cases.

Conclusion:
Local growth curves classified more SGA neonates as non‑SGA compared with a universal standard, missing many with placental malperfusion. Universal standards may better identify pathologic FGR and improve prenatal risk detection