Haemoglobin level, proportion of haemoglobin Bart's and haemoglobin Portland in fetuses affected by homozygous α0-thalassemia from 12 to 40 weeks' gestation.

OBJECTIVES

To determine haematological parameters in fetuses affected by homozygous α(0)-thalassemia.

METHODS

This was a cross-sectional retrospective study reviewing 546 blood samples (268 fetal and 278 neonatal cord) being collected between 1993 and 2006, from 12 weeks' gestation onwards for any indication, including the prenatal diagnosis of homozygous α(0)-thalassemia, other haematological disorders, hydrops or aneuploidy. The proportion of haemoglobin (Hb) fractions was determined by electrophoresis of haemolysate on cellulose acetate in all samples.

RESULTS

There were significant differences in the haematological parameters between homozygous α(0)-thalassemia (n = 183) and control (n = 363) which were either heterozygous α(0)-thalassemia (alpha thalassemia trait) or normal. In homozygous α(0)-thalassemia, the median Hb level, proportion of Hb Bart's (γ(4)) and Hb Portland 1(ζ(2)γ(2)) were 6.4 g/dL, 77.5% and 22.5%, respectively. While the Hb level and the proportion of Hb Bart's increased significantly with gestation, the proportion of Hb Portland 1 decreased. The Hb level contributed by Hb Portland 1 remained around 1.4 g/dL throughout gestation. The proportion of mild, moderate and severe anaemia in the affected fetuses was 27.5, 32.7 and 39.8%, respectively. There was no significant difference in these proportions across different gestation (P = 0.231). There were no differences in the haematological parameters between hydropic and non-hydropic fetuses.

CONCLUSION

Although the degree of anaemia is mild in around one-quarter of the affected fetuses, the contribution by Hb Portland 1 (ζ(2)γ(2)) to the Hb level was very low throughout gestation, and the affected fetuses may therefore be at risk for hypoxia.