Study on the reference range of angle between superior mesenteric artery and abdominal aorta in normal fetuses at 21-41 weeks of gestation

ObjectiveTo measure the angle between superior mesenteric artery(SMA) and abdominal aorta(AA)(SMA-AA angle) to calculate its 95% reference value range, and explore its correlation with fetal gestational age(GA), head circumference(HC), abdominal circumference(AC) and femoral length(FL).

MethodsThe single pregnancy pregnant women diagnosed by obstetric ultrasound examination in The Fourth Affiliated Hospital of Anhui Medical University from January to April 2021 were selected according to the inclusion criteria.The SMA-AA angle in each fetus was measured, and the correlation of the angle with gestational age, head circumference, abdominal circumference and femur length were investigated.

ResultsA total of 260 fetuses were included in the study.The mean value of SMA-AA angle of normal fetuses at 21-41 weeks of gestation was(57.75±7.27)°(range from 40.90° to 73.60°), and the 95% reference range was 43.50°-72.00°.There was no significant correlation between the SMA-AA angle and fetal GA, HC, AC and FL(r=0.007, 0.025, 0.022 and 0.025, respectively, P>0.05).The reproducibility of ultrasound measurement of the SMA-AA angle of normal fetuses at 12-41 weeks of gestation was good(the number of data points outside the interval of 95% agreement of inter-observers was 2.86%, and the number of data points outside the interval of 95% agreement of intraobserver was 0.04%).

ConclusionsThe SMA-AA angle in normal fetus at 21-41 weeks of gestation remains relatively stable, and is not significantly correlated with fetal GA, HC, AC and FL.