To investigate the influence of the length of time of supine ultrasound examination on the parameters of umbilical artery blood flow in the late pregnant fetus.

From February 2019 to June 2019, the ultrasound data of 93 pregnant women with the third-trimester pregnant were analyzed retrospectively.Fetal umbilical artery systolic/diastolic (S/D) ratio, resistance index (RI), pulsatility index (PI) and fetal heart rate (HR) were acquired at the beginning of the ultrasound examination and those after the routine ultrasound examination (the examination of fetal, placenta and amniotic fluid). Forty-seven pregnant women from 29 to 31 weeks of gestation were assigned to around 30-week gestation group, while 46 pregnant women from 35 to 37 weeks of gestation were assigned to around 36-week gestation group.Sixty-five pregnant women with normal S/D ratio at the beginning were assigned to the initial normal group, while 28 pregnant women with abnormal S/D ratio at the beginning were assigned to the initial abnormal group.Fetal umbilical artery S/D ratio, RI, PI and HR at the beginning of the ultrasound and after the routine ultrasound examination were compared using paired sample test within around 30-week gestation group, around 36-week gestation group, initial normal and initial abnormal group, respectively.

There was no significant difference in fetal umbilical artery S/D, RI PI and HR in the pregnant women at around 30-week gestation(all P>0.05). RI before the 36 week pregnant group was 0.56±0.05, and increased to 0.58±0.05 after the routine examination (t=-2.190, P=0.034). The S/D, RI and Pi of umbilical artery increased from 2.36±0.31, 0.57±0.06, and 0.84±0.11 to 2.50±0.42, 0.59±0.06, and 0.88±0.14 in the initial normal group (t=-3.087, -3.002, -2.287, respectively; P=0.003, 0.004, 0.025, respectively), of which 16 S/D increased to abnormal; the RI of umbilical artery increased from 0.67 in the initial abnormal group (28 women) after routine examination). The difference was statistically significant (t=2.616, P=0.014). The ratio of S/D decreased to normal after routine examination in the initial abnormal group (14/28), which was higher than that in the initial normal group (16 / 65). The difference was statistically significant (χ²=5.771, P<0.05).

Umbilical artery blood flow parameters should be measured at the beginning of the ultrasound examination in the third-trimester pregnant women.Umbilical artery Doppler ultrasound should be performed repeatedly if the pregnant woman has abnormal S/D ratio at the beginning of the examination.

Umbilical artery blood flow; The third-trimester pregnancy; Supine position