DISQ 5: Counseling women with isolated ‘soft’ markers at 18–24 weeks

Abstract

Fetuses with Down syndrome are more likely to have a thickened nuchal fold, echogenic intracardiac foci and renal pyelectasis compared with unaffected fetuses1. The same is true for trisomy 18 and choroid plexus cysts. Increasingly, calculating person-specific risk for Down syndrome from several different parameters (age, hormones, ultrasound markers) is becoming the norm. However, to alter the risk of Down syndrome in the presence of an isolated ultrasound ‘soft’ marker adds another layer of complexity that has not yet been resolved satisfactorily. Although the likelihood ratios of Down syndrome in the presence of soft markers have been calculated from a systematic review of the literature1, the confidence intervals are huge, reflecting the differences over the years in the quality of both equipment and sonographers. The critical issue here is the term ‘isolated soft marker’. How much skill and experience does one need to be able to say that a soft marker is truly isolated? Important malformations like atrioventricular septal defects can be missed2. Do you believe that an apparently isolated soft marker found on a routine anatomy scan is an indication for referral to a specialist in obstetric ultrasound? An unqualified YES was the answer of 79% of the panel. Three experts (10%) answered NO, two advocated referral only in the presence of increased nuchal fold thickness and one suggested that a referral is warranted only if nuchal translucency-based screening was not performed earlier. Having performed a scan yourself and found an isolated soft marker in a woman with a low risk of Down syndrome (< 1 : 300), for which of the following would you discuss an increased risk of trisomies with her? Our panel reached the consensus that fetuses in whom an isolated ‘soft marker’ has been found on routine ultrasound examination should have a further assessment by an expert who is also trained to provide appropriate counseling. It is less clear what action should be taken by such an expert once it has been confirmed that the soft marker is indeed isolated. According to our expert panel, nuchal thickening should trigger discussion about trisomies. However, there was almost a 50 : 50 split with regard to the other three common soft markers. Several experts commented on the need to provide individualized counseling that combines the background (a priori) risk with the additional risk from soft markers. Whether any currently proposed formulae for such risk calculations are methodologically robust enough for routine clinical use remains a matter for debate.