Antenatal diagnosis of AVSD is of particular clinical and medicolegal importance because of its strong association with trisomy 21. Despite multiple potential anomalies in babies with trisomy 21, non-cardiac sonographic markers (for example, renal pelvic dilatation) are often subtle and are frequently missed during screening. Therefore, the ability of fetal ultrasound to detect congenital heart disease accurately in this setting is particularly important.1,6
There is an understandable and widely held view that AVSD, particularly in the presence of a chromosomal anomaly, should not be missed at a screening scan. In low risk fetal populations, however, detection rates during screening for congenital heart disease as a whole are reported to vary from 13–92%.4,7,8
The antenatal detection rate for a consecutive series of liveborn patients with AVSD, a lesion potentially diagnosable on the standard four chamber view, has not been reported before. In our series 70% of AVSDs were diagnosed only after birth despite the majority of referring centres in our study having received basic on-site fetal echocardiography training. Although not significant, the rate of detection in babies with trisomy 21 was less than for chromosomally normal infants.
Once complex cases known to be associated with AVSDs in infants without trisomy9
were removed from the analysis the detection rate was similar at 25% and 23% for infants with and without trisomy 21, respectively.
It is beyond the scope of this paper to discuss detection rates for other congenital cardiac lesions; however, the echocardiographic hallmark of the AVSD is a common atrioventricular valve, which even on a good four chamber view can appear superficially normal.
By implication AVSDs may be more difficult to detect at standard screening than lesions with more obvious structural pathology. Although training for obstetric screening units was almost universal in this series and this undoubtedly translated to a greater awareness of congenital heart disease, perhaps technical proficiency can be gained only by exposure to a large number of abnormal cases. For the average obstetric screening unit this is an unrealistic expectation. Effective screening for this important lesion may require a different strategy.
The antenatal detection rate for AVSD by standard ultrasound screening in the four chamber view is poor overall, with a trend towards being even poorer in the presence of trisomy 21.