Objective: To assess with Doppler colour flow imaging whether a brain-sparing effect is present in all cerebral arteries of the circle of Willis in the small for gestational age fetus, to determine which cerebral flow velocity parameter is most discriminating in this pathological condition, and to relate this parameter to the umbilical artery pulsatility index.
Design: Prospective, cross-sectional, matched case-control study.
Setting: Academic department of obstetrics and gynaecology.
Subjects: Twenty-eight small for gestational age fetuses and 28 normal controls at 24 to 38 weeks of gestation.
Interventions: Blood flow velocity waveforms from the umbilical and fetal intracerebral arteries were studied with Doppler colour flow imaging for measurement of peak systolic, end-diastolic and time averaged velocities, and calculation of the pulsatility index.
Main outcome measures: Comparison of intracerebral and umbilical artery waveform parameters between small for gestational age fetuses and controls.
Results: Acceptable flow velocity waveforms were obtained in the intracerebral circulation in more than 85%. In small for gestational age fetuses, all intracerebral arteries displayed reduced downstream impedance. The end-diastolic velocities of the middle and anterior cerebral artery are the most discriminative factors between small for gestational age fetuses and controls. The highest sensitivity was reached for the umbilical artery pulsatility index.
Conclusions: Doppler colour flow imaging allows easy identification of fetal intracerebral arterial vasculature. Whereas for the intracranial vasculature, the end-diastolic blood flow velocities in the anterior and middle cerebral artery are the most sensitive parameters discriminating between small for gestational age and controls, umbilical artery pulsatility index remains the best indicator for the small for gestational age fetus.