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Soft Markers
Introduction

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Introduction

Screening for Down’s syndrome

There are several established methods to screen for Down’s syndrome. We regard soft marker scanning at 18-22 weeks as a weak screening method because it has poor sensitivity for a relatively high false positive rate, and gives results late in pregnancy. This guideline therefore aims to recommend a method for dealing with soft markers discovered during a routine anomaly scan, rather than recommend soft marker scanning as a method of screening.

Significance

The absence of soft markers on ultrasound has little relevance for the risk of trisomy, and many publications have overstated the significance of seeing a soft marker. Reporting these findings can cause considerable anxiety. Furthermore, it can lead to invasive tests being undertaken unnecessarily, with the potential of miscarriage associated with these procedures.

Consent

All investigations, including ultrasound scans, require the consent of the expectant mother, who should be informed of the possible findings and consequences of any test. Mothers need to be aware that the findings of soft markers may prompt a discussion of chromosomal anomalies.

Expertise

This booklet details a list of soft markers, their identification, the possible implications and further areas to be considered. The imaging part of this screening process is within the competence of all professionals currently undertaking mid pregnancy anomaly scanning. This booklet aims to ensure that professionals feel able to include and exclude soft markers, and complete their mid trimester examination, usually at a single ultrasound scan. This should reduce the need for internal or external referral, and increase the reassurance which can be given to the expectant mother.

The following are considered to be soft markers. They are dealt with in more detail in the following sections.

  • Nuchal pad Infinity Symbol 6 mm 4-5
  • Echogenic bowel 6-7
  • Echogenic foci in the fetal heart 8-9
  • Short femur < 3rd centile 10-11
  • Dilated renal pelvis (pyelectasis) > 5 mm 12-13
  • Choroid plexus cysts 14-15

Other findings such as a 2 vessel cord, the head shape and variations in the hands and feet are not considered soft markers in this context.

Indications to report and offer karyotyping

  • Nuchal pad alone, or
  • The finding of any 2 of the other soft markers listed above, or
  • A single soft marker if present in a woman who is otherwise high risk,
    because:
    • screen positive from Down’s syndrome screening (>1:250), or
    • >=3 years of age (in the absence of previous Down’s screening)
  • CPCs when seen with other trisomy 18 risk factors

Additional reporting

  • Pyelectasis should be reported and followed up according to local
    protocols.
  • Echogenic bowel should be reported and referred for Consultant opinion
    and management.
  • Other soft markers, if seen in isolation, DO NOT need to be reported
    or explained, as there is no evidence that they have any significant impact
    on the pregnancy.

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Reference

1. Smith-Bindman R, Hosmer BS, Feldstein MD, Deeks J, Goldberg JD. (2001) Second trimester ultrasound to detect fetuses with Down Syndrome – A meta analysis. JAMA:285 (8), Abstract

 
 
© Perinatal Institute 2011