With the development of ultrasound technology and improvement of people's understanding regarding fetal ARSA, the prenatal detection rate of ARSA is increasing daily. In this study, 112 fetuses were diagnosed with ARSA by prenatal ultrasound. Trisomy 21 syndrome has been reported in 14–20% of fetuses with ARSA [15, 16]. Thus, ARSA is closely related to chromosomal abnormalities. In this study, karyotype analysis and SNP-array were used to detect the genetic etiology of 112 fetuses with ARSA. Chromosomal abnormalities were detected in three cases (2.7%, 3/112) by karyotype analysis. The rate of chromosome abnormalities in this study was significantly lower than those reported in the literature . However, SNP-array was used to detect five additional cases of pathogenic CNV, including two cases of microdeletion, two cases of microduplication, and one case of LOH. Conventional karyotype analysis can only detect chromosome fragment abnormalities of over 5-10MB, while SNP-array can detect low copy number abnormalities of over 10KB and normal copy number abnormalities such as LOH [18, 19]. Therefore, SNP-array has advantages in the etiological detection of fetuses with ARSA.
In this study, a total of eight cases of pathogenic CNV were detected in 112 fetuses with ARSA, including trisomy 21, trisomy 18, large fragment 22q12 duplication, 22q11.21 microdeletion, 17p12p11.2 microduplication, 16p11.2 microduplication, 2q13 microdeletion, and LOH of 1p36.21p35.2 and 4p15.2p11. The presence of ARSA may increase the risk of trisomy 21 syndrome. In this study, one case of trisomy 21 syndrome was detected in a fetus with ARSA, which is consistent with previous studies [8, 17, 20–22]. ARSA has also been reported in 22q11 deletion syndrome (22q11DS) . The manifestations of patients with 22q11DS were varied, mainly including congenital heart defects, thymus hypoplasia, parathyroid dysfunction with hypocalcemia, and developmental delay [24, 25]. Moreover, patients with 22q11DS may have vascular abnormalities, such as the right aortic arch and ARSA [26–29]. One case of 22q11DS was also detected in a fetus with ARSA in this study. The 17p12p11.2 microduplication contains the RAI1 gene , which can lead to the occurrence of Potocki-Lupski syndrome. The main clinical characteristics of Potocki-Lupski syndrome are abnormal heart development, low intelligence, triangular face, high zygomatic arch, and palatal dysplasia . To date, no studies have reported the relationship between Potocki-Lupski syndrome and ARSA; however, in this study, one case of 17p12p11.2 microduplication was detected in a fetus with ARSA. Similarly, there is no relevant research on the relationship between 16p11.2 microduplication, 2q13 microdeletion, and LOH of 1p36.21p35.2 and 4p15.2p11 and ARSA, which needs to be confirmed by more researchers in the future.
Chaoui et al. , Rembouskos et al. , and Gul et al.  each reported a case of isolated ARSA with trisomy 21. Therefore, some scholars believe that ARSA can be used as one of the soft ultrasound markers for prenatal screening of fetal chromosome abnormalities, and prenatal chromosome examination should be recommended even if it is found alone. However, other studies do not recommend invasive prenatal testing for fetuses with isolated ARSA unless accompanied by other ultrasound abnormalities [17, 33]. Combined with the results of our study, two fetuses with isolated ARSA were detected with 16p11.2 microduplication, and LOH of 1p36.21p35.2 and 4p15.2p11, respectively. The rate of pathogenic CNV in isolated ARSA group was 4.2% (2/48), the rate of pathogenic CNV in ARSA combined with other ultrasound abnormalities was 9.3% (6/64). Although the rate of the pathogenic CNV in ARSA combined with other ultrasound abnormalities was higher than that of the isolated ARSA group, there was no statistical significance between the two groups. Therefore, SNP-array should be recommended for ARSA with other ultrasound abnormalities in fetuses, although the possibility of isolated ARSA with pathogenic CNV should not be ignored.
In addition to being associated with pathogenic CNV, ARSA is also closely associated with congenital heart defects . Borenstein et al.  reported that the incidence of ARSA with congenital heart defects reached 16%, but due to the small number of cases, the types of congenital heart defects commonly associated were not counted. In this study, the incidence of ARSA combined with congenital heart defects was slightly lower, and 17 cases (15.2%, 17/112) were combined with congenital heart defects, among which ventricular septal defect was the most common type. The results of this study showed that 34.8% (39/112) of fetuses with ARSA were associated with extracardiac abnormalities, among which the most common complication was abnormal soft ultrasound markers, and the risk of pathogenic CNV increased with other ultrasound abnormalities. In this study, pathogenic CNV was detected in six fetuses with ARSA combined with other ultrasound abnormalities, including three fetuses with congenital heart defects, two fetuses with abnormal soft ultrasound markers, and one fetus with strephenopodia. Therefore, when prenatal ultrasound detects ARSA in the fetus, it is necessary to be highly alert to the possibility of other ultrasound abnormalities and carefully observe the fetus for other ultrasound abnormalities.
VUS has always been controversial, and the detection rate of VUS depends on the type of microarray chip and the population studied [36, 37]. Some studies have reported that VUS accounts for 1–12% of the population , and this study found that VUS accounts for 1.8% (2/112), which is consistent with the literature. The two fetuses with VUS in this study had good growth and development during postnatal follow-up. The C-type vascular ring formed by ARSA belongs to the incomplete vascular ring, which partially surrounds the trachea and esophagus and usually does not cause compression to the trachea and esophagus . In this study, 96 fetuses with ARSA excluding pathogenic CNV had good growth and development after birth and during follow-up after genetic counseling. However, there were four cases of fetuses with ARSA combined with other ultrasound abnormalities. Although the genetic analysis was normal, there were severe ultrasound abnormalities, and the parents chose to terminate the pregnancies. In recent years, next-generation sequencing has been used to detect single-gene mutations and copy number variation [39–41], which may provide a more comprehensive prenatal genetic diagnosis for fetuses with ARSA and a better evaluation of fetal prognosis.
In conclusion, ARSA is a common soft ultrasound marker. Isolated ARSA in fetuses has a low probability of pathogenic CNV. However, when ARSA is complicated with other ultrasound abnormalities, the risk of pathogenic CNV is greatly increased. Prenatal genetic counseling and SNP-array should be recommended to better assess fetal prognosis.