Estimation of Fetal Foot Length and Femur-to-Foot Length Ratio in Indian Population for Estimating Gestational Age on Sonography During Second Trimester (17-25 Weeks)

Background Assessing accurate fetal gestational age is vital in ascertaining the accurate growth of the fetus. Even if there are multiple ways to evaluate the fetal gestational age using ultrasonography, foot length measurement of the fetus can be utilized as an alternate tool to ascertain the age of gestation accurately. The length of the fetal femur and foot was estimated and recorded, and their ratio was calculated in this study. This parameter helps in distinguishing dysplastic short limbs from those shortened due to constitutional factors or due to intrauterine fetal growth retardation. Ultrasonography was used in this study to assess the association between gestational age and fetal foot length. The aim of the study is to derive normogram correlating gestational age (in weeks) with fetal foot length and to derive the femur-to-foot length ratio in women with 17-25 weeks of gestation. Materials and methods In our study, 150 healthy women with singleton pregnancy and 17-25 weeks of gestation underwent routine ultrasound examination in the Department of Radio Diagnosis, Meenakshi Medical College Hospital and Research Institute. In addition to the routine parameters, foot length and femur-to-foot length ratio were estimated. Results A strong correlation (positive) was observed in this study with Pearson's correlation coefficient of 0.996 seen between gestational age and foot length, and 0.930 between foot length and femur length, both with a statistically significant <i>p</i> value < 0.0001. The femur-to-foot length ratio ranged from 0.9 to 1 in all cases. Conclusion The study revealed a robust correlation, which was linear, between gestational age and foot length, thereby supporting the use of fetal foot length as an added biometric measure to estimate gestational age. Additionally, the study highlights that the femur-to-foot length ratio approximates 1, with a ratio below 0.92 serving as a reliable indicator for detecting most cases of dysplasia.