Antenatal soft markers on ultrasound

Antenatal soft ultrasound markers are fetal sonographic findings that are generally not abnormalities as such but are indicative of an increased age-adjusted risk of an underlying fetal aneuploidic or certain non-chromosomal abnormalities.

Most of the described features do not constitute a structural defect and may be detected on antenatal screening, typically during a second trimester (morphology) scan. Many are transient.

What is included or not appears to depend on the respective authorities in each region, and remains dynamic, with certain markers periodically emerging, or conversely losing favor. 

The following are markers in common use at the time of writing. The list includes features having an association with:

An increased risk of aneuploidy and in some cases non-chromosomal abnormalities 

• increased nuchal thickness: >6 mm

• fetal ventriculomegaly: >10 mm

• hypoplastic/absent nasal bone

• echogenic intracardiac focus (EIF) 

• choroid plexus cyst

• echogenic bowel 

• shortened fetal long bones: less than 3^rd centile for gestational age

  • shortened femur

  • shortened humerus

• aberrant right subclavian artery (ARSA)

An increased risk of non-chromosomal abnormalities when seen in isolation

• fetal pyelectasis/fetal renal pelvic dilatation: antero-posterior diameter of the renal pelvis >4-5 mm

• single umbilical artery

• enlarged cisterna magna

Soft markers of undefined association

• clenched fists

• rocker bottom feet

• sandal gap

• strawberry skull

Correct interpretation of these often requires correlation with other risk factors such as history, maternal age, and maternal serological results.