Description

The measurement of the thoracic circumference is taken transversely at the level in which a four chambered heart can be visualized.

The circumference of the thorax can be measured:

(1) directly using computer planimeters

(2) indirectly from measurement of the anteroposterior diameter and the maximum transverse diameter at right angles to the anteroposterior axis, as follows:

thoracic circumference in cm =

= 0.5 ((anteroposterior diameter in cm) + (transverse diameter in cm)) * π

Fetal thoracic circumference

 week 50th percentile 5th percentile 95th percentile 16 9.1 cm 6.4 cm 11.9 cm 17 10 cm 7.3 cm 12.8 cm 18 11 cm 8.2 cm 13.7 cm 19 11.9 cm 9.1 cm 14.6 cm 20 12.8 cm 10 cm 15.5 cm 21 13.7 cm 11 cm 16.4 cm 22 14.6 cm 11.9 cm 17.3 cm 23 15.5 cm 12.8 cm 18.2 cm 24 16.4 cm 13.7 cm 19.1 cm 25 17.3 cm 14.6 cm 20 cm 26 18.2 cm 15.5 cm 21 cm 27 19.1 cm 16.4 cm 21.9 cm 28 20 cm 17.3 cm 22.8 cm 29 21 cm 18.2 cm 23.7 cm 30 21.9 cm 19.1 cm 24.6 cm 31 22.8 cm 20 cm 25.5 cm 32 23.7 cm 20.9 cm 26.4 cm 33 24.6 cm 21.8 cm 27.3 cm 34 25.5 cm 22.8 cm 28.2 cm 35 26.4 cm 23.7 cm 29.1 cm 36 27.3 cm 24.6 cm 30 cm 37 28.2 cm 25.5 cm 30.9 cm 38 29.1 cm 26.4 cm 31.9 cm 39 30 cm 27.3 cm 32.8 cm 40 30.9 cm 28.2 cm 33.7 cm

from Chitkara (1987)

When this data is analyzed in JMP, the following equations are obtained:

50th percentile for thoracic circumference in cm =

= (0.9077692 * (week of gestation)) - 5.377538

5th percentile for thoracic circumference in cm =

= (0.9086923 * (week of gestation)) - 8.135385

95th percentile for thoracic circumference in cm =

= (0.9083077 * (week of gestation)) - 2.660615

week of gestation =

= (1.1015794 * (50th percentile thoracic circumference in cm)) + 5.9243484

= (1.1004618 * (5th percentile thoracic circumference in cm)) + 8.9532066

= (1.1009273 * (95th percentile thoracic circumference in cm)) + 2.926839