With the progression of pregnancy, umbilical cord blood flow diastolic steady growth, and the fetal umbilical artery peak systolic velocity
With the progression of pregnancy, umbilical cord blood flow diastolic steady growth, and the fetal umbilical artery peak systolic velocity (S) and diastolic velocity (D) ratio (S/D value) is reduced, so that the fetal placental circulation to reduce the resistance, contribute to fetal development. The results of the research for many years show that the S/D value of fetal umbilical artery is an ideal parameter to monitor the condition of uterus. Umbilical artery resistance index (RI) can be used if D=0 or negative value. It can also be used to determine the pulsatility index of the umbilical cord in the amniotic fluid in the free segment of fetal Doppler in the absence of fetal respiratory movement and the stability of the spectrum. Clinical analysis showed that the S/D value of fetal umbilical artery decreased with the increase of gestational weeks. The second trimester in 3 - 0 for police such as S/D& ge3 0 should be S/D < were monitored after 32 weeks of pregnancy; 3 / 0 late pregnancy S/D value & le2. 5 when the fetus was considered safe. The higher the S/D value, the greater the risk. Intrauterine fetal death occurs when D=0 or negative. The clinical value of S/D is more common in the following situations: IUGR, gestational diabetes mellitus, pregnancy induced hypertension, etc.. It is also reported that D value can be equal to zero when fetal chromosome abnormality. In addition, the prenatal diagnosis of umbilical cord around the neck of the fetus, if the S/D value is high, should relax cesarean section indications, prevent labor pull cord thinner, blood flow interrupted the occurrence of acute fetal distress cause fetal death.
In the process of clinical application, the abnormal S / D value, before 30 weeks of gestation, a large number of papers on the S / D& ge3.0 & ge3.0 boundary is abnormal, suggesting that the cord blood flow resistance increased, < 3 for normal.
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