Objective: To evaluate the effect of maternal weight on the intra- and inter-observer reproducibility of third-trimester ultrasonography fetal measurements. Methods: The present prospective study, performed at a tertiary hospital, enrolled patients at between 35⁺⁰ weeks and 36⁺⁶ weeks of singleton pregnancies between January 1, 2015, and July 1, 2016. Fetal ultrasonography measurements were evaluated twice by a first observer and a third time by a second observer. Intra- and inter-observer consistency were analyzed using the Cronbach α reliability coefficient, and measurement reproducibility was compared with patients stratified by a body mass index (BMI, calculated as weight in kilograms divided by the square of height in meters) of below 25 or at least 25. Results: The study included 197 patients (133 with BMI <25 and 64 with BMI ≥25). Among patients with a BMI below 25, the reliability coefficients for bi-parietal diameter, head circumference, abdominal circumference, and femur length measurements were 0.97, 0.95, 0.98, and 0.96, respectively, for intra-observer consistency, and were 0.97, 0.93, 0.98, and 0.95, respectively, for inter-observer consistency. Among patients with a BMI of at least 25, these values were 0.97, 0.96, 0.98, and 0.97, respectively, for intra-observed consistency, and 0.97, 0.94, 0.98, and 0.96, respectively, for inter-observer consistency. Conclusion: High intra- and inter-observer reproducibility was observed for third-trimester fetal ultrasonography measurements, including for patients who were overweight.