Thalassemia is one of the most common monogenetic diseases in the south of China and Southeast Asia. Hemoglobin Bart’s hydrops fetalis syndrome was caused by a homozygous Southeast Asian deletion (–/–) in the HBA gene. Few studies have proved the potential of screen for Bart's hydrops fetalis using fetal cell-free DNA. However, the number of cases is still relatively small. Clinical trials of large samples would be needed.

In this study, we aimed to develop a noninvasive method of target-captured sequencing and genotyping by the Bayesian method using cell-free fetal DNA to identify the fetal genotype in pregnant women who are at risk of having hemoglobin Bart hydrops fetalis in a large-scale study.

In total, 192,173 couples from 30 hospitals were enrolled in our study and 878 couples were recruited, among whom both the pregnant women and their husbands were detected to be carriers of Southeast Asian type (–/αα) of α-thalassemia. Prenatal diagnosis was performed by chorionic villus sampling, amniocentesis, or cordocentesis using gap–polymerase chain reaction considered as the golden standard.

As a result, we found that the sensitivity and specificity of our noninvasive method were 98.81% and 94.72%, respectively, in the training set as well as 100% and 99.31%, respectively, in the testing set. Moreover, our method could identify all of 885 maternal samples with the Southeast Asian carrier and 36 trisomy samples with 100% of sensitivity in T13, T18, and T21 and 99.89% (1 of 917) and 99.88% (1 of 888) of specificity in T18 and T21, respectively.

Our method opens the possibility of early screening for maternal genotyping of α-thalassemia, fetal aneuploidies in chromosomes 13/18/21, and hemoglobin Bart hydrops fetalis detection in 1 tube of maternal plasma.