Aim and objective: Our aim of the study was to determine the role of foetal kidney length to predict gestational age at third trimester. Material and Methods: We were conducted a prospective, observational study between the duration of January 2021 to June 2022. In our study, we were enrolled 140 pregnant women who having third trimester of pregnancy. We were observed kidney length, femur length, HC, AC and BPD during our study. Result: Among 140 patients, Multigravida patients were highly observed compared to primigravidae. We observed that gestational age with last menstrual period was highly significantly positively correlated with mean kidney length (r=0.958) compared to right kidney length, left kidney length, MKL, femur length , BPD , AC ,HC and weight. Based on mean kidney length, we were predicted (r2=91%) equation to determine gestational age at third trimester. Conclusion: Foetal kidney length can be utilised as an additional criterion for estimating gestational age in the third trimester since the results of the current study have demonstrated a substantial link between renal length and gestational age, particularly in the third trimester.