(158) Should amniocentesis be universally offered in cases of isolated fetal VSD?

Cases of prenatally diagnosed ventricular septal defect (VSD) are traditionally offered invasive prenatal testing due to associated aneuploidy, namely trisomy 21 (T21). In the absence of endocardial cushion involvement, the association between isolated fetal VSD and T21 is less clear and can present challenges in counselling at the mid trimester anomaly sonogram. Given our obstetric population is unscreened for aneuploidy risk, we sought to investigate if isolated fetal VSD is significantly associated with T21.

Study Design:

Cases with prenatally diagnosed isolated VSD at the mid trimester anomaly scan during a 15 year period (2006-2021) were identified from a fetal anomaly register after ethical approval. Cases where first trimester screening or NIPT had been undertaken prior to diagnosis of VSD, or those with soft markers for T21 were excluded. The location of the VSD, rate and results of invasive testing and pregnancy outcome were determined.

Results:

71 cases of isolated fetal VSD were identified. The location of the VSD is shown in table 1. After diagnosis, seven patients opted for NIPT.  One case was reported as high risk for T21 and subsequently confirmed with amniocentesis. A total of 13 (18%) had invasive testing and three were confirmed as T21. One case was identified with a maternally inherited deletion and one had a mosaic ring chromosome 15.  All three mothers with a fetal diagnosis of T21 were aged 35 and older.  The prevalence for T21 at 20 weeks gestation for our study cohort was estimated at 0.6%. 

Conclusion:

Isolated fetal VSD is associated with an abnormal karyotype or microarray in 7% (5/71) of cases, and T21 in 4% (3/71) of cases. However, all cases of T21 had an increased a priori risk, therefore we cannot conclude that the additional finding of an isolated fetal VSD further refines risk. Nonetheless, the finding in this study of a rate of 4% for T21 in association with an isolated fetal VSD should encourage a higher uptake for invasive testing. These data can be used to assist counselling in unscreened obstetric populations and provide reassurance in women with a low a priori risk.