A Practical Prenatal Ultrasound Classification System for Lower Limb Anomalies-PRELLIM Classification.

OBJECTIVE

To address the current lack of a prenatal classification system for fetal lower limb anomalies, we developed and evaluated the PRELLIM (PREnatal Lower LIMb impairment) classification.

METHOD: A systematic literature review was conducted to identify existing classifications. Based on sonographic features, we developed the PRELLIM classification and applied it to a retrospective cohort of fetuses with isolated lower limb anomalies assessed between 2007 and 2024 at Amsterdam UMC's fetal medicine unit.

RESULTS

No standardized prenatal classification system for lower limb anomalies was found. PRELLIM distinguishes isolated and non-isolated anomalies and categorizes them into clinically relevant subgroups (absent/short, duplication, fusion, contracture, bowing and other). It was applied to 643 fetuses with isolated lower limb anomalies. Contractures were most common (n = 599; 93.2%), followed by poly(syn)dactyly (n = 26; 4.0%), reduction defects (n = 9; 1.5%), bowing (n = 5; 0.8%), and a case of sirenomelia (0.1%). Three additional cases (0.4%) were classified as "other": two lymphangiomas and one amniotic band with lower leg constriction.

CONCLUSION

PRELLIM is the first prenatal classification tailored to sonographically detectable lower limb anomalies. It aims to enhance diagnostic consistency, improve interdisciplinary communication, and support prenatal counseling and decision-making.