Fetal sonographic cardiothoracic ratio at midpregnancy as a predictor of Hb Bart disease

The objective of this study is to evaluate the efficacy of sonographic card iothoracic ratio at midpregnancy in predicting fetal hemoglobin Bart diseas e. Among 17,254 pregnant women screened for severe thalassemia between Tune 1994 and November 1998, 345 pregnant women at risk for having a fetus with hemoglobin Bart disease underwent ultrasonographic examination and cordoce ntesis at 18 to 21 weeks' gestation. Before cordocentesis, the cardiothorac ic ratio was determined and recorded. The definite fetal diagnosis was base d on fetal blood analysis with high performance liquid chromatography. Amon g 345 pregnancies in which sonographic examination and cordocentesis were p erformed, 70 fetuses were affected by hemoglobin Bart disease. The mean car diothoracic ratio was significantly higher than that of unaffected fetuses (0.55 versus 0.45, Student's t-test, P < 0.001). The sensitivity and specif icity of the cardiothoracic ratio in prediction were calculated for various cutoff values. On the basis of the receiver operating characteristic curve , the best cutoff value was 0.50 (greater than 0.50 considered abnormal), g iving the sensitivity of 98.6% and a specificity of 98.9%. In conclusion, t he cardiothoracic ratio has very high accuracy in predicting hemoglobin Bar t disease in pregnancies at risk. This finding suggests that invasive diagn ostic method should be reserved for only the fetuses who have a cardiothora cic ratio of 0.5 or more; however, further studies are needed to confirm th is observation.