Presented by: Dr. Farzad Afzali Kasra medical imaging center

 An early stage in fetal adaptation to hypoxemia increased blood flow in DV to protect the brain, heart, and adrenals central redistribution of blood flow ( brain- sparing reflex) reduced flow to the peripheral and placental circulations

Under physiologic conditions, 60 to 70 percent of umbilical venous blood in the human fetus is distributed to the liver and the remainder to the heart. With chronic hypoxemia, this proportion may be modulated so that a larger proportion of umbilical venous blood can bypass the liver to reach the heart

◦ Middle cerebral artery ◦ Aorta ◦ Umbilical artery ◦ Uterine artery ◦ IVC ◦ Ductus venosus

 The middle cerebral artery (MCA) in the fetal brain Normally high-impedance Most accessible to U/S imaging More than 80% of cerebral blood

 Average of both MCAs must be calculated for more precise result.  Compression of the fetal head causes increasing arterial resistance.( false negative of IUGR)

 The best predictor for fetal acidemia is PI of thoracic aorta.  The best predictor of fetal hypoxia is PI of MCA.

The damage that obliterate small muscular arteries in placental tertiary stem villi absent flow or even reversed flow, suggestive more than 70% damage of placenta. commonly associated with severe IUGR and oligohydramnios Waveforms obtained from the placental end of cord show more end-diastolic flow, thus lower RI & PI, than waveforms obtained from the abdominal cord insertion. (No significance on clinical practice)

◦ Velocimetry of uterine artey should be obtained after the vessel crosses the hypo gastric artery and vein, at the uterus-cervical junction, before it divides to cervical and uterine branches. ◦ The best predictor of PIH is notch in the uterine artery & RI>61.5 % after 22 w of gestation.

Uterine artery

 Venous indices reflect : ventricular function Fetal hypoxia Myocardial lactic acidosis

Decrease cardiac output secondary to myocardial dysfunction Rise in CVP Increase in reverse flow in atrial systole Transmitted down venous system - the further from the heart the greater degree of cardiac dysfunction

DV ‘a’ wave decrease Reverse EDF UA -- Reverse ‘a’ wave DV Pulsatile UV Constriction of cerebral circulation Death within 96 hours

◦ At the level of AC measuring, ductus venosus can be identified as it branches from hepatic vein. ◦ It has high speed flow with biphasic waveform. ◦ The first phase corresponding ventricular systole, the second phase to early diastole and nadir to the atrial kick.

◦ Umbilical vein displays pulsatility in first trimester but this disappears with advancing gestation in the pregnancy unaffected by FGR

◦ In clinical practice, it is necessary to carry out serial Doppler investigations to estimate the duration of fetal blood flow redistribution. ◦ The onset of abnormal venous Doppler results indicates deterioration in the fetal condition and iatrogenic delivery should be considered

PI of MCA/PI of TA must be more than 0.9 before 30,less than 0.8 before the 34 & less than 0.75 before the 36 weeks of pregnancy. PI of MCA/ PI of UA must be >1.08 during pregnancy. The larger values are abnormal & termination may be considered after weeks of pregnancy.

Preterm growth restricted fetuses with elevated umbilical artery Doppler resistance have an overall perinatal mortality rate of 5.6 percent. This rate increases to 11.5 percent when end-diastolic velocity is absent. and rises to 38.8 percent when venous Doppler indices become abnormal (predominantly due to an increase in the rate of stillbirth).

Reverse flow in the umbilical artery, along with pathologic waveform in the venous system are the best predictor of sever fetal distress, so termination of pregnancy must be considered as soon as possible.