Fetal cerebral haemodynamic adaptation: a progressive mechanism? Pulsed and color Doppler evaluation.

The importance of studying, by Doppler ultrasound, the cerebral haemodynamics to monitor the fetal response to the hypoxia is well known, but there is not a general agreement about the anatomical landmarks for the middle cerebral artery. Seventy-one normal fetuses and fifteen IUGR fetuses were studied. The umbilical artery and the middle cerebral artery (MCA) were evaluated by color Doppler ultrasound. The well-known decrease of the pulsatility index from the umbilical artery was observed throughout pregnancy. This velocimetric pattern did not occur in the IUGR fetuses. Four IUGR fetuses showed the ARED (absent or reversed and diastolic flow) pattern. The MCA was evaluated at the origin (M1) and at the distal tract (M2). PI values from M1 and M2 decreased during the pregnancy. A significant difference was detected between M1 and M2 PI values from the 26th to the 37th week of gestation. The M1 brain sparing effect was detected in the IUGR fetuses. Two ARED fetuses, observed during labor, showed the M2 sparing effect. The different Doppler patterns found in M1 and M2 could be due to the functional differences existing between these tracts. As a matter of fact, M1 and M2 supply different parts of the fetal brain, which develop in different periods of fetal life. These findings, if ulteriorly confirmed, could offer new perspectives for the monitoring of high risk fetuses.