### Description

The abdominal circumference is calculated from a transverse plane through the abdomen; the plane is usually at the ductus venosus and should contain the gastric bubble but be above the superior poles of the kidney. Abdominal circumference measurements can be used during the second and third trimesters. It can be used in conjunction with other fetal estimates or when other parameters cannot be measured for technical regions.

It can be determined:

(1) directly using computer planimeters

(2) indirectly from measurement of the maximum diameter of the abdomen in the sagittal plane and the maximum diameter in the coronal plane.

abdominal circumference in cm =

= 0.5 ((sagittal diameter in cm) + (coronal diameter in cm)) * π

 menstrual age in weeks abdominal circumference in cm 12 4.6 12.5 5.3 13 6 13.5 6.7 14 7.3 14.5 8 15 8.6 15.5 9.3 16 9.9 16.5 10.6 17 11.2 17.5 11.9 18 12.5 18.5 13.1 19 13.7 19.5 14.4 20 15 20.5 15.6 21 16.2 21.5 16.8 22 17.4 22.5 17.9 23 18.5 23.5 19.1 24 19.7 24.5 20.2 25 20.8 25.5 21.3 26 21.9 26.5 22.4 27 23 27.5 23.5 28 24 28.5 24.6 29 25.1 29.5 25.6 30 26.1 30.5 26.6 31 27.1 31.5 27.6 32 28.1 32.5 28.6 33 29.1 33.5 29.5 34 30 34.5 30.5 35 30.9 35.5 31.4 36 31.8 36.5 32.3 37 32.7 37.5 33.2 38 33.6 38.5 34 39 34.4 39.5 34.8 40 35.3

Equations derived from analysis of this data in JMP:

menstrual age in weeks =

= (0.0075425 * ((abdominal circumference in cm) ^ 2) + (0.6019323 * (abdominal circumference in cm)) + 9.2207099

predicted abdominal circumference in cm for given fetal age =

= ((-0.009998 * ((menstrual week gestation) ^ 2) + (1.6140951 * (menstrual week gestation)) - 13.31578

Hadlock (1982) developed equations for abdominal circumference and menstrual age:

abdominal circumference in cm =

= -10.4997 + (1.4256 * (menstrual age in weeks)) - (0.00697 * ((menstrual age in weeks) ^2))

menstrual age in weeks =

= 7.6070 + (0.7645 * (abdominal circumference in cm)) + (0.00393 * ((abdominal circumference in cm) ^2))

Limitations:

• Abdominal circumference may be reduced with intrauterine growth retardation, resulting in underestimates of gestational age.