Nonvisualized, dilated or even a small fetal stomach can be associated with a variety of anomalies and poor fetal outcome. Therefore, we attempted to evaluate the stomach circumference (SC)/abdominal circumference (AC) ratio to assess normal limits of fetal stomach size. A total of 363 fetuses ranging from 15 to 39 weeks' gestation were prospectively evaluated with ultrasonography. The SC was measured from a plane that is perpendicular to the fetal longitudinal axis at the level where the largest axial circumference of the stomach was obtained using a digitizer. The AC was also measured at the same section and the ratio was calculated by dividing the SC by the AC and multiplying by 100. The SC increased linearly from 15 to 24 weeks and showed fluctuations in size thereafter to 39 weeks. A strong correlation was noted between gestational age and both SC (r: 0.842, P < 0.0001) and AC (r: 0.975, P < 0.0001). The SC/AC ratio was normally distributed with a mean of 20.4 +/- 3.9% and ranged between 14.8% and 27.03% throughout pregnancy (r: 0.021, P > 0.05). Although the fetal stomach is a dynamically changing organ, the SC/AC ratio can be considered as a potentially useful parameter in assessing fetal stomach size.