RESUMEN
Objective To evaluate the efficacy of the ratio of the fetal cardiac diameter to biparietal diameter( CBR) as a predictor of homozygous α-thalassemia-1 . Methods Single mid-pregnancies ( 15-22weeks) at risk of homozygous α-thalassemia-1 were enrolled . A total of 251 singleton pregnancies were recruited ,in which 63 cases were homozygous α-thalassemia-1 fetuses and the rest were unaffected . The CBR and cardiothoracic ratio(CTR) were measured by two-dimensional ultrasound . Then the accuracy of these variables were analyzed and compared with each other by ROC curves . Results ①The CBR and CTR in affected fetuses were significantly higher than those in the unaffected( P ＜0 .01) . ②With CBR＞0 .43 and CTR ＞ 0 .52 as the best cut off values ,the sensitivity and specificity of predicting homozygous α-thalassemia-1 fetuses in 15-22 gestational weeks were 95 .74% , 92 .06% and 94 .15% , 85 .71% , respectively ;the area under ROC curve were compared with Z test and there was no significant difference between them ( Z ＝ 1 .500 , P ＝ 0 .1335) . ③ When CBR and CTR were combined ,the sensitivity and specificity of the prediction were significantly increased ( the sensitivity of series experiment : 99 .75% ,the specificity of parallel experiment : 98 .87% ) . Conclusions CBR is a novel , effective and noninvasive predictor of homozygous α-thalassemia-1 in mid-pregnancy whose prediction efficiency is the same as traditional CTR . The measurement of CBR is easier to standardize and is not affected by thoracic lesions such as pleural cavity ,pericardial effusion and skeletal dysplasia . If combined with CTR ,it may play an important role in improving the prenatal detection rate of homozygous α-thalassemia-1 fetuses .