Fetal foot biometry in mid-gestation: values for foot length, toe lengths, and proportional indices in a Turkish population

Aims: To establish gestational age-specific reference values for fetal foot length, first toe length, second toe length, second-to first toe length ratio, and foot length-to-femur length ratio in mid-gestation, and to evaluate their relationships with gestational age and conventional fetal biometric parameters. Methods: This prospective cross-sectional study included 155 singleton pregnancies between 18 and 24 weeks of gestation. Fetal foot, first toe, and second toe lengths were measured sonographically. The second-to-first toe length ratio and foot length-to femur length ratio were calculated. Reference values were generated, and regression and correlation analyses were performed. Results: Fetal foot, first toe, and second toe lengths increased progressively with advancing gestation. Foot length showed strong positive correlations with gestational age and conventional biometric parameters, including biparietal diameter (BPD), head circumference (HC), abdominal circumference, femur length, and estimated fetal weight (all p<0.001). First and second toe lengths demonstrated similar significant associations with gestational age and fetal biometric measurements (all p<0.001). In contrast, the second-to-first toe length ratio and foot length-to-femur length ratio remained relatively stable throughout the study period and showed no clinically meaningful relationship with gestational age. Intraobserver reproducibility was excellent for all measurements (ICCs: 0.958-0.991). No significant gender-related differences were observed in any fetal foot measurements. Conclusion: Fetal foot, first toe, and second toe lengths increase during mid-gestation and are strongly associated with conventional fetal biometric parameters. Conversely, the second-to-first toe length ratio and foot length-to-femur length ratio remain stable. The reference values generated in this study provide normative data for fetal foot biometry and may support future clinical and research applications.