Objective: Fetuses affected by homozygous alpha-thalassemia-1 develop anemia as early as the first trimester. Our objective was to study hemodynamic indices in affected fetuses at 12-13 weeks of gestation to determine whether these would be useful in the prediction of anemia.
Design: Prospective observational study.
Subjects: Women referred before 14 weeks of gestation for the prenatal diagnosis of homozygous alpha-thalassemia-1.
Methods: Transabdominal and/or transvaginal Doppler sonography was performed to measure the flow velocities in the fetal ascending aorta and pulmonary artery at 12-13 weeks. The Doppler indices were compared between those that were subsequently confirmed to be affected by homozygous alpha-thalassemia-1 and those that were unaffected.
Results: Between June 1997 and April 1998, 60 eligible women were recruited. Doppler examination was successful in 58 fetuses. Of these, 22 were subsequently confirmed to be affected by homozygous alpha-thalassemia-1. The diagnosis was made by chorionic villus sampling and DNA analysis in two affected fetuses and by cordocentesis and hemoglobin evaluation in 20 affected fetuses. Hemoglobin concentrations could be measured in ten fetuses and these ranged from 4 to 8 g/dl. The affected fetuses had significantly higher peak velocities at the pulmonary valve and ascending aorta and a larger inner diameter of the pulmonary valve than that in unaffected fetuses. The total cardiac output was increased by one-third in affected fetuses and was mainly due to an increase of the right-side cardiac output.
Conclusion: In the early stage of anemia, the fetus responds mainly by increasing its right-side cardiac output. However, there is extensive overlap of the values of cardiac output between the affected and the unaffected fetuses, precluding its use in the prediction of anemia.