Fetal biometric measurements including biparietal diameter (BPD), head circumference (HC), femur length (FL), and abdominal circumference (AC) are an essential part of fetal imaging and these measurements are incorporated into commercially available algorithm which provides for an estimated fetal weight, which can be used to determine whether there is adequate fetal growth for gestational age.  Fetal cardiothoracic (C/T) circumference ratio is also used to assess fetal cardiac size. 


Biparietal diameter (BPD) - measure from the beginning of the fetal skull to the inside aspect of the distal fetal skull ("outer to inner") at the level of the cavum septum pelucidum


Head Circumference (HC) - measured as an ellipse in a horizontal section at the level of the thalamus and the cavum septi pellucidi


Femur Length (FL) - measures the longest bone in the body and reflects the longitudinal growth of the fetus


Abdominal Circumference (AC) - measured at the outer edge of the circumference of the body plane in which the umbilical vein or stomach can be visualized in a tangential section


Cardiothoracic (C/T) Circumference Ratio - This is an important parameter used to assess fetal cardiac size.  It is the ratio of the cardiac circumference to the thoracic circumference which slowly increases throughout gestation.