Soft Markers on a Scan

Why some markers are no longer chased

A soft marker is a finding on the 20-week scan that is not an abnormality in itself but has, historically, been associated with a raised chance of a chromosomal condition. For years, spotting one triggered a conversation about further testing. That is no longer the national position for several of them, and the change is set out plainly in the NHS Fetal Anomaly Screening Programme handbook.

The reason is arithmetic. With better first-trimester screening and NIPT, a lone soft marker in an otherwise normal scan adds so little to the chance calculation that acting on it generates far more anxiety and intervention than information. So the programme drew an explicit line.

The findings the programme treats as normal variants

The handbook states: "If one or more of the normal variants listed below are seen, the woman does not need referral for further assessment as part of the NHS FASP:

• choroid plexus cysts
• dilated cisterna magna
• echogenic foci in the heart
• 2 vessel cord"

These are exactly the findings that used to generate a referral and often a diagnostic test. Choroid plexus cysts — small fluid pockets in the part of the brain that makes cerebrospinal fluid — and echogenic foci in the heart, sometimes described to parents as a bright spot on the heart, are the two most commonly seen and the two that most commonly cause alarm. Neither, on its own, is a reason for further assessment under the national programme.

The findings that do need referral, with their measurements

The handbook is equally specific about the other group: "the scan findings listed below need to be reported and the woman referred for further assessment:

• nuchal fold (greater than or equal to 6.0mm)
• ventriculomegaly (atrium greater than or equal to 10.0mm)
• echogenic bowel (with density equivalent to bone)
• renal pelvic dilatation antero-posterior (AP) measurement (greater than 7.0mm)
• small measurements of HC, AC and/or FL (below the 5th centile on fetal biometry charts)"

Two details are worth reading twice. The nuchal fold at 20 weeks is a different measurement from the nuchal translucency at 12 weeks, with a different threshold — 6.0mm rather than 3.5mm — and they are not interchangeable. And echogenic bowel only counts when its brightness is "equivalent to bone"; a bowel that looks slightly bright is not the same finding.

A separate list, for growth rather than chromosomes

Some findings are followed up for a completely different reason, and this is where most confusion arises. The handbook explains: "Although not part of NHS FASP, some scan findings can be associated with an increased risk of fetal growth restriction (FGR). The Royal College of Obstetricians and Gynaecologists (RCOG) guidance and the NHS England Saving Babies' Lives Care Bundle (SBLCB) require additional assessment for FGR."

The findings on that list are: "echogenic bowel", "estimated fetal weight below the 10th centile", and "single umbilical artery (2 vessel cord)".

So a two-vessel cord appears on both lists — as a normal variant needing no chromosomal referral, and as a trigger for growth surveillance. If you have been told your two-vessel cord needs no further action and also been booked for extra growth scans, both statements are correct and they come from different frameworks.

What the 20-week scan is and is not looking for

The NHS scan checks for signs of 11 specific physical conditions, and the handbook is candid that "other conditions can also be detected but these are not part of the NHS FASP. This is because the data is insufficient to confidently predict the standard for detection that should be achieved."

It also confirms that "all significant findings of the scan are reported", and that "any woman who does not wish to be informed of the 11 physical conditions or other unexpected findings should consider not having the scan". You cannot have a partial scan.

Placental position and amniotic fluid are checked at the same appointment, but the handbook notes these are "not part of the NHS FASP" — they are "good clinical practice" alongside it.

If a marker on the referral list is found

Referral means a more detailed look, usually in a fetal medicine unit, and a conversation about whether any further testing is wanted. It does not automatically mean an invasive test. Several of the findings on the referral list — renal pelvic dilatation in particular — most often turn out to be isolated and to resolve, with the follow-up being a repeat scan later in pregnancy and sometimes a check on the baby after birth.

What changes the conversation is whether a marker is isolated or seen alongside others. A single finding in an otherwise entirely normal scan, in a pregnancy with a lower-chance first-trimester screening result, is a very different situation from two or three findings together.

What to ask

Ask which specific finding was recorded and its measurement in millimetres, whether it appears on the normal variant list or the referral list in the FASP handbook, and whether your earlier screening result was lower-chance or higher-chance. Those three answers between them define almost the whole picture, and they are all recorded in your notes.

Why the guidance changed, and why that is reassuring

It is worth understanding the logic, because being told a finding "does not need any action" can feel like being fobbed off. Screening only helps when acting on a result leads to better outcomes than not acting. For an isolated choroid plexus cyst or echogenic focus in the heart, the chance added to an already-completed first-trimester screening result is so small that the referrals, the anxiety and the invasive tests that followed did more harm than the finding.

The NHS programme therefore made a deliberate decision to stop reporting these as actionable, and wrote the list down so that practice is the same everywhere. A sonographer telling you that a bright spot on the heart is a normal variant is quoting a national document, not reassuring you informally.

If you want to know more after being told a normal-variant finding was seen, you are entitled to ask what exactly was recorded and to have it explained. What you should not need to do is push for a referral the programme has decided against.