Doppler velocimetry in cerebral vessels of small for gestational age infants

Using the duplex Doppler system, blood velocity was measured serially at two sites of the anterior cerebral artery (ACA) and in the middle cerebral artery (MCA) during the first 3 days of life, in eight term, small for gestational age (SGA) infants (birthweight, 2179 +/- 230 g; mean +/- S.D.), and 13 term, appropriate for gestational age (AGA) infants (3376 +/- 441 g). All infants in both groups had normal Apgar scores and none manifested signs of respiratory distress. At 1 h post partum, the average MCA mean velocity in the SGA group (25.8 +/- 6.9 cm/s) was higher than that in the AGA group (19.6 +/- 5.7 cm/s), whereas the average values of the two ACA sites did not differ between the groups. A significantly increased value of the average mean velocity as compared to the value at 4 h post partum was reached earlier in the AGA group at all three vessel sites. The pulsatility index (as defined by Gosling) was lower at all vessel sites up to 72 h in the SGA group. Pulse pressure was significantly lower in the SGA group due to increased diastolic blood pressure. We suggest the results imply a state of cerebral vasodilation in the SGA infants and a poor ability to respond with an increased perfusion in the frontal regions supplied by the ACA. Changes in blood pressure and cerebral haemodynamics appear to exist in SGA infants in the absence of postnatal hypoxia which might explain the vulnerability of the growth-retarded infant to perinatal hypoxia.