Fetal Thigh Circumference Nomograms Across Gestational Ages: A Retrospective Study

Background/Objectives: Fetal thigh circumference (ThC) may be a valuable parameter for assessing fetal growth. Thus, this study aimed to establish reference ranges for ThC across gestational ages (GA). Methods: This retrospective study included singleton pregnancies between 12 and 38 weeks of gestation. ThC measurements were obtained during routine ultrasound examinations. GA was confirmed through the last menstrual period and first-trimester crown-rump length measurements. Percentile ranges for ThC were calculated for each gestational week, and statistical analyses evaluated the relationship between ThC and GA. Results: 48,841 singleton pregnancies were included. A positive correlation was observed between ThC and GA, with ThC values increasing progressively from 12 to 38 weeks. The study established the 10th, 50th, and 90th percentile ranges for ThC, providing reference values for clinical assessments. Conclusions: This study provides reference ranges for fetal ThC across a wide GA range, highlighting its potential as a tool in prenatal care. ThC may offer an additional parameter for monitoring fetal growth, especially when standard measurements are challenging. Further research should investigate the integration of ThC with other fetal growth parameters to enhance its clinical utility. Additionally, these nomograms can be used to assess their usefulness in certain conditions, such as intrauterine growth restriction (IUGR), macrosomia, and congenital skeletal dysplasias.