Middle cerebral artery Doppler study in fetuses with homozygous alpha-thalassaemia-1 at 12-13 weeks of gestation

Objective: Fetuses affected by homozygous alpha-thalassaemia-1 are anaemic from the first trimester of pregnancy. We investigated middle cerebral artery Doppler velocimetry in these affected fetuses at 12-13 weeks of gestation to assess its use in predicting fetal anaemia.

Methods: Women referred for the prenatal diagnosis of homozygous alpha-thalassaemia-1 before 14 weeks of gestation were recruited. All fetuses underwent pulsed Doppler examinations following colour flow mapping at 12 or 13 weeks of gestation. Homozygous alpha-thalassaemia-1 was diagnosed by DNA or haemoglobin study. The middle cerebral artery Doppler indices were compared between the affected fetuses and fetuses unaffected by homozygous alpha-thalassaemia-1.

Results: Between 1998 and 2000, 80 eligible women were recruited. Of these, 19 fetuses were affected by homozygous alpha-thalassaemia-1. Two of them showed hydropic changes at the time of Doppler study. The affected fetuses had significantly higher middle cerebral artery peak systolic velocity (V(max)) (36% increase) and time-averaged maximum velocity (V(tamx)) (33% increase).

Conclusion: The increase of cerebral blood flow in affected fetuses is consistent with our previous finding of an increased forward flow in the ductus venosus, cardiac dilatation and an increase of cardiac output to preferentially shunt more oxygenated blood to the brain as a compensatory mechanism. However, extensive overlap of the middle cerebral artery flow velocity values between affected and unaffected fetuses precludes its use in predicting anaemia at 12-13 weeks' gestation.