The normal growth of cross-sectional areas of the aorto-iliac segment in human fetuses - an anatomical, digital, and statistical study

The intraluminal size of the aorto-iliac segment is relevant in both the clinical and echographic settings. The aim of this study was to compile both the absolute and relative age-specific reference intervals for cross-sectional areas (CSAs) of the aorto-iliac segment. Using the methods of anatomical dissection, digital-image analysis (Leica QWin Pro 16) and statistical analysis (Student's t test, one-way ANOVA, post-hoc RIR Tukey test, linear regression), the growth in CSA (in mm2) of the abdominal aorta, the common, external, and internal iliac arteries in 124 (60 males, 64 females) spontaneously aborted human fetuses aged 15-34 weeks was examined. No significant sex differences were found. In the age range of 4-9 months, the distal CSA of the abdominal aorta ranged from 0.87±0.34 to 19.18±3.36 mm2. The CSA of the common iliac artery varied from 0.37±0.22 to 4.30±1.54 mm2 on the right, and from 0.36±0.16 to 3.80±1.44 mm2 on the left. The sum of the CSAs of the right and left common iliac arteries grew proportionately to the distal CSA of the abdominal aorta; the latter being significantly larger than the former. On both sides, however, the CSA of the internal iliac artery was approximately twice that of the external iliac artery. Between the ages of 4 and 9 months, the CSA of the external iliac artery ranged from 0.10±0.06 to 1.32±0.52 mm2 on the right, and from 0.08±0.03 to 1.19±0.42 mm2 on the left. The CSA of the internal iliac artery increased from 0.23±0.14 to 2.59±1.22 mm2 on the right, and from 0.21±0.14 to 2.27±1.11 mm2 on the left. Bilaterally, the sum of the CSAs of the internal and external iliac arteries was significantly smaller than the CSA of the common iliac artery. The relative CSA of each artery decreased until the age of 6 months, after which their values were gradually increasing until the age of 9 months. The aorto-iliac segment does not reveal sex differences in its cross-sectional area. The cross-sectional area of the internal iliac artery is approximately twice the size of the external iliac artery. The aorto-iliac segment observed proximally to distally reduces its cross-sectional area, thereby resulting in an increase in blood velocity.