Objective:To study the blood flow parameters in fetal inferior adrenal artery during the middle and late trimester of normal pregnancy and to determine the normal reference range . Methods: A total of 604 pregnant women from 18 to 36 weeks who received routine prenatal ultrasonography were enrolled in this study. Fetal IAA peak systolic velocity (PSV)

end-diastolic velocity (EDV)

pulse index (PI) and resistance index (RI) were measured by pulse Doppler in oblique coronal section of both kidneys.The normal reference range related to GA was established. Pearson correlation analysis was used to test the correlation between IAA hemodynamic parameters and gestational age. Scatter plots were drawn for each parameter and GA

and various regression models were fitted to select the best fitting curve. Results: Finally

594 fetuses were included. The resistance parameters of IAA (PI

RI) were negatively correlated with gestational weeks (P < 0.05

r=-0.73

0.81)

and the Cubic curve was the best fit. There was no significant correlation between the speed parameter PSV of IAA and gestational weeks (P > 0.05). There was a slight positive correlation between)

EDV and gestational weeks (P < 0.05

r=0.24). The fitting degree of Cubic curve was the best. Conlusion: This study established a normal reference range of normal fetal IAA blood flow parameters

which is helpful to further evaluate fetal hemodynamics.