Soft Markers in Second Trimester


Reviewed by IndianRadiologist

Soft Markers in Second Trimester of Pregnancy 

Soft Markers are Minor Ultrasound abnormalities

Variants of normal

Do not constitute a structural defect

Can increase the risk of an aneuploidic fetus 

List of 2nd Trimester Soft Markers 

Nuchal Fold Thickening

Choroid Plexus Cyst

Nasal Bone – Absence or Hypoplasia

Ventriculomegaly

Echogenic Cardiac Focus 

Renal Pyelectasis

Echogenic Bowel

Short Humerus 

Single Umbilical Artery 

Nuchal Fold Thickening

Normally measures 5 mm at 15-18 W and 6 mm at 18-24 W



Measurement should not be greater than 6 mm in 18-24 W scan

Proposed etiology is due to lymphatic obstruction and congenital heart disease

Most sensitive and predictive indicator for Down’s Syndrome

Strong association with Down’s Syndrome?

Needs invasive testing to rule out aneuploidy even if isolated  

Choroid Plexus Cyst     


These cysts have no epithelial lining, and as such these are not true cysts, but rather spaces within the choroid plexus filled with clear fluid (CSF) and cellular debris material.

Association is with Trisomy 18, Klinefelter Syndrome and Aicardi Syndrome

Seen at the atria of the lateral ventricles

Uncommonly seen after 25 W (they regress by 25 W)

Association with Trisomy 18 - About 33% of T18 fetuses will have choroid plexus cysts.

Conversely, only 0.27% incidence of T18 fetuses have choroid plexus cyst as an isolated finding

Fetuses with isolated cysts are almost always normal and hence there is no need of invasive testing  

Nasal Bone   

Nasal bone is often seen as a bright echogenic line.

It is best measured at around the 11th to 14th weeks of gestation ?In fetuses with Down syndrome, 6 (37%) of 16 did not have detectable nose bones compared with 1 (0.5%) of 223 control fetuses

*Absent Nasal bone needs karyotyping  

Echogenic Intra Cardiac Focus

Considered to be mineralization/ calcification in the papillary muscle

Common in Asian population

Association with Down’s Syndrome & T13

Commonly seen in the LV, RV

Echogenic focus or multiple foci has more significance then EF in the LVLR is 2.

If risk less than 1/600, then no Karyotyping

If isolated – then no karyptyping

Can disappear by the third trimester  

 

Ventriculomegaly

Mean measurement is 7.6 mm

Constant during pregnancy trimesters

Measurement above 10 mm is abnormal

Significant in high risk groups / aneuploidy risk

Other conditions of brain to be ruled out – Fetal MRI can be done 

 

Echogenic Bowel

0.25 -1.5% of all scans

it has been postulated that it relates to loss of water from meconium in the 3rd trimester, meconium containing bowel may appear echogenic as a normal finding 

Grading: 

Grade 1 : mildly hyper echoic to liver / less than bone 
Grade 2 : moderately hyper echoic compared to liver / as echogenic as bone 
Grade 3 : markedly hyper echoic compared to liver / greater than bone

It has been described as a prenatal marker for 
> Cystic fibrosis?
> Chromosomal aneuploidy (Down’s Syndrome)             
> Infections like CMV
Hyperechogenic bowel therefore carried a 16-fold greater risk for Down syndrome


Check for CMV – congenital infections 
Check parental status for Cystic Fibrosis (2%)
Rule out Aneuploidy? (LR is 6)
Follow up to evaluate for IUGR   

 

Renal Pyelectasis

4 mm at 18 - 20 weeks

persistent fetal pyelectasis : > 7 mm in the 3rd trimester

In the majority of cases, it is physiological and resolves spontateously

Solitary Finding: No invasive testing.

Weak association with Trisomy 21 

 

Single Umbilical Artery 

The occurrence of  a single umbilical artery is thought to be due to secondary atresia or atrophy rather than primary agenesis of the artery

No association with aneuploidy

Associated with renal anomalies, velamentous insertion of cord, and sirenomelia 

Short Humerus 

humeral length falls below the 5th centile or less than 0.9 predicted by the bi-pareital diameter

Association with aneuploidy, especially  DS, and fetal skeletal dysplasias   

 

INTERPRETATION 

Minor fetal abnormalities or soft markers are common and they are not usually associated with any handicap, unless there is an underlying chromosomal defect.

Detailed structural scan is done of the fetus to rule out abnormalities/ other soft markers

Risk increases as multiple markers or abnormalities are seen in the fetus

It is best to base counseling on an individual estimated risk (related to maternal age, Triple marker)

Isolated Abnormality like thickened nuchal fold & Absent Nasal Bone need Amniocentesis, while echogenic bowel needs other tests.

If there is a constellation of findings or abnormal structural scan or abnormal Triple Marker – Amniocentesis is offered