ObjectiveTo study the model to predict thymus volume with two-dimensional section diameters among fetuses. MethodsFrom September 2010 to March 2012, 210 singleton pregnant women suspected with fetal abnormality by prenatal ultrasonic testing were confirmed using MRI technology. Three two-dimensional section diameters of thymus were measured and the volume was calculated. No abnormal fetuses regarded as the standard, theoretical normal volume of fetal thymus was calculated. Paired t-test was used to compare the actual thymus volume with its corresponding theoretical normal value, and thus the fetuses were divided into two groups of normal and dysplasia so as to establish predictive model respectively. With two-dimensional section diameters as independent variables and thymus volume as dependent variable, the linear regression model was established. According to the model, the thymus volume was predicted and the error rate was calculated by formula: error rate=(predicted value-actual value) /actual value×100%. The Pearson correlation coefficient of error rate and fetal gestational age was calculated. ResultsThe models of normal and dysplasia groups to predict thymus volume were lnV=0.016d1+0.030d2+0.086d3+5.707+ε (R2=0.510) and lnV=0.048d1+0.036d2+0.016d3+6.011+ε (R2=0.447). The average absolute values of predicted error rate were 4.34% and 5.34% and decreased with fetal gestational age (normal r=-0.264, P=0.007; dysplasia r=-0.182, P=0.060). ConclusionThe prediction effects of above models are not so good and the model accuracy increases with fetal gestational age. Normal fetuses' model of different gestational age should be established to predict thymus volume by conducting large sample size study in the future. The modeling approach has certain practicability and clinical value and can be applied in ultrasonic technique.