The purpose of the study was to observe the elastic properties of the aorta in normal fetuses by M-mode echocardiography.
This was a prospective cross-sectional study performed in 402 normal fetuses during 20-37 weeks of gestation. The elastic properties of the ascending aorta, thoracic aorta, and abdominal aorta were assessed by diameter strain (DS) which was determined by M-mode echocardiography. DS was defined as 100 × (D - D)/D. Correlations between DS and gestational age and combined cardiac output were assessed by linear regression analysis.
We successfully acquired 377 (93.8%) normal fetal measurements. DS of the ascending aorta, thoracic aorta, and abdominal aorta declined as the gestational age proceeded (b = -0.683, -0.358 and -0.263, p < 0.001), while it increased with combined cardiac output (b = 0.041, 0.03, and 0.017, p < 0.001). DS in the ascending aorta and thoracic aorta were higher than those in the abdominal aorta (p < 0.001), while there was no significant difference between the ascending aorta and thoracic aorta. The reproducibility for DS measurements by M-mode echocardiography was good.
Our results demonstrated a decline in DS with gestational age and variable aortic strain from the proximal to distal segments in the normal fetuses. Intrauterine changes in arterial elastic properties might reflect the maturation of fetal circulation.

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