Presented by:

Dr. Farzad AfzaliKasra medical imaging center

An early stage in fetal adaptation to An early stage in fetal adaptation to

hypoxemiahypoxemia

• 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.

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 35-37 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.