### Introduction

### Materials and methods

### 1. Inference

### 2. Observed data in Korean women

### 3. Validation of inferential equations

*Ultrasonography in obstetrics and gynecology*[11]. After gathering the sonographic data from 194 patients, we calculated the median value of each biometric parameter (BPD, AC, and FL) for every gestational week. These data were named 'observed data'. Biometric values were calculated using inferential equations and were named 'calculated data'. Mean absolute errors were evaluated to compare the difference between the observed and calculated data.

### Results

### 1. Inference

### 2. Validation of inferential equations with known reference values

^{2}values which show the degree of ability to implicate the relationships were over 0.98 in all three biometric parameters, and the

*P*-values were all less than 0.001. When comparing these equations to our inferential equations which are: BPD (cm)=0.25×GA (wk), AC (cm)=1.0×GA (wk)-5.0, FL (cm)=0.20×GA (wk), it is true that the coefficients and constants are not exactly the same. However, given that the purpose of this study is not to find "exact" formulae, but "quick and simple" ones, we decided that such differences were in acceptable range.