Table 2 Regression formula used to generate ultrasound biometry charts and tables of biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL), and estimated fetal weight (EFW)

BPD

 Mean = − 24.624 + 3.739* GA - 0.0004972* GA3

 SD = 1.994 + 0.053* GA

HC

 Mean = − 94.476 + 14.273* GA - 0.0020276* GA3

 SD = 8.182 + 0.121*GA

AC

 Mean = − 78.497 + 11.708* GA - 0.0009802* GA3

 SD = 2.059 + 0.461* GA

FL

 Mean = − 32.653 + 3.499* GA - 0.0005433* GA3

 SD = 1.975 + 0.028* GA

EFW

 Mean = 0.0095699*GA**4.4937733

 SD = 0.00265083*GA**3.287346