Week 4: Ultrasound findings- softmarkers

Question 1

Differentiate between a fetal anomaly and a soft marker

Answer 1

Fetal anomaly
-Structural abnormality
-Adverse health outcomes
-Increase risk for aneuploidy or genetic disorder

Soft marker
-Typically reflect normal variation
-Often are transient
-Increase the risk for aneuploidy
-Ex: absent nasal bone, increased NT, short long bones

Question 2

What percent of second trimester fetuses have at least one soft marker identified by ultrasound?

Answer 2

~15% of pregnancies

Question 3

If an absent or hypoplastic nasal bone is detected on US, what are 2 things to consider that might not indicate an aneuploidy?

Answer 3

1. Ethnic variation: for example African Americans more likely to have hypoplastic nasal bone without aneuploidy
2. Ultrasound may reflect delayed maturation rather than true absence of nasal bone

Question 4

What percentage of euploid fetuses have an absent nasal bone?

Answer 4

~2.5%

Question 5

What are the 7 US soft markers associated with increased risk for Down syndrome?

Answer 5

1. Echogenic intracardiac focus
2. Echogenic bowel
3. Single umbilical artery
4. urinary tract dilation
5. shortened long bones
6. Thickened nuchal fold
7. Absent/hypoplastic nasal bone

Question 6

What soft marker is associated with cystic fibrosis?

Answer 6

Echogenic bowel

Question 7

What soft marker is associated with choroid plexus cyst?

Answer 7

T18

Question 8

What is a likelihood ratio?

Answer 8

Ratio used to express a change in odds, calculated using the test sensitivity and specificity

**LR of 1.0 means US finding does not change risk for condition

Question 9

What does a positive likelihood ratio mean?

Answer 9

-A positive likelihood ratio is typically greater than one
-It increases the odds of having the condition in patients with the US finding
-A LR greater than 1 produces a post-test probability that is higher than the pre-test probability

Question 10

What is a negative likelihood ratio?

Answer 10

-A negative likelihood ratio is typically less than one
-It decreases the odds of having the condition in patients with the US finding
-A LR less than 1 produces a post-test probability which is lower than the pre-test probability

Question 11

LRs from 1.5-5 mean what?

Answer 11

Confer a small additional increase in the likelihood of the outcome

Question 12

LRs from 5-10 mean what?

Answer 12

Confer a moderate additional increase in the likelihood of the outcome

Question 13

LRs >10 mean what?

Answer 13

Confer a substantial additional increase in the likelihood of the outcome

Question 14

Variability in positive and negative LR estimates are influenced by what?

Answer 14

-Differences in patient populations studied
-Variability in soft marker definitions
-Variability in detection of soft markers by US
-Whether or not for any isolated soft marker the lack of another soft marker is incorporated into the positive LR estimate

Question 15

T/F the presence of multiple soft markers is exponentially more concerning

Answer 15

True!

However, there aren’t any studies that have examined the interrelationship between presence of markers and therefore they are assumed to be independent in LR apart from short femur/humerus