Head Cube to Abdominal Cube Ratio

 

Fetal Gestational Age Range: 12 to 40 weeks

 

Ultrasonic Measurements:

(1) A transverse section of the cranium at the level of the thalamus and cavum septi pellucidi, with measurement of the biparietal diameter and occipitofrontal diameter in cm.

(2) A transverse section of the abdomen through the fetal liver at the level of the umbilical vein perpendicular to the fetal spine, with a measurement of the long axis and short axis of the ellipse.

 

Variability:

(1) variability in head cube and abdominal cube increase with gestational age

(2) variability in ratio of head cube to abdominal cube decrease with gestational age

(3) variability in all three parameters was greatest from 12-17 weeks menstrual age

 

head cube =

= (((biparietal diameter in cm) * (occipitofrontal diameter in cm)) ^ 1.5)

 

abdominal cube =

= (((long abdominal diameter in cm) * (short abdominal diameter in cm)) ^ 1.5)

 

head cube to abdominal cube ratio =

= (head cube) / (abdominal cube)

 

predicted head cube =

= 0.0085 * (((weeks of gestation from LMP) - 5) ^ (3.84 - (0.01465 * ((weeks of gestation from LMP) - 5))))

 

lower value for head cube

• 12-17 weeks: (predicted head cube) * 0.444

• 18-40 weeks: (predicted head cube) * 0.712

 

upper value for head cube

• 12-17 weeks: (predicted head cube) * 1.556

• 18-40 weeks: (predicted head cube) * 1.288

 

predicted abdominal cube =

= 0.0228 * (((weeks of gestation from LMP) - 6.5) ^ (3.23 - (0.003 * ((weeks of gestation from LMP) - 6.5))))

 

lower value for abdominal cube

• 12-17 weeks: (predicted abdominal cube) * 0.102

• 18-40 weeks: (predicted abdominal cube) * 0.526

 

upper value for abdominal cube

• 12-17 weeks: (predicted abdominal cube) * 1.898

• 18-40 weeks: (predicted abdominal cube) * 1.474

 

predicted head cube to abdominal cube ratio =

= 2.416 * (((weeks of gestation from LMP) - 5) ^ (-0.00118 - (0.0077 * ((weeks of gestation from LMP) - 5))))

 

lower value for head cube to abdominal cube ratio

• 12-17 weeks: (predicted ratio) * 0.23418

• 18-40 weeks: (predicted ratio) * 0.652

 

upper value for head cube to abdominal cube ratio

• 12-17 weeks: (predicted ratio) * 1.76618

• 18-40 weeks: (predicted ratio) * 1.438