Maternal Serum Screening Flashcards
What are the real implications of the results from a screening test?
Positive Test = risk increased
Negative Test = risk decreased
Positive Predictive Value
The likelihood a pregnancy is affected when screening indicates a positive or high-risk result
Negative Predictive Value
The likelihood a pregnancy is unaffected when screening indicates a negative or low risk result
What does the First Trimester Screen test screen for?
Down syndrome
trisomy 18
What is a normal NT (nuchal translucency) measurement?
< 3.0 mm
What are the implications of an increased NT?
Increased NT is an independent risk factor for increased risk of aneuploidy, even if analytes are normal.
All of hte anlytes are produced by the placenta in FTS except for…
AFP
What are the 2 main analytes tested during FTS and what is their typical pattern?
Pregnancy-associated plasma protein A (PAPP-A): Rises throughout pregnancy
Human chorionic gonadotropin (hCG): rises rapidly until 10 weeks gestation then declines
How long is normal, healthy pregnancy?
40 weeks
What levels of PAPP-A & hCG are associated with trisomy 18?
both are decreased
(all analytes are low in trisomy 18)
hCG is also low during 2nd trimester screen for trisomy 18
What levels of PAPP-A & hCG are associated with Down syndrome?
hCG tends to be increased and PAPP-A tends to be decreased
hCG is also high in 2nd trimester for Downs
What value for MoM is considered normal?
1
What risk does poorly controlled diabetes pose to a fetus?
open neural tube defects
When is AFP ordered and what does its level tell us?
Second trimester
Increased AFP is associated with ONTD
Most analytes are made by the placenta, where is AFP made though?
the yolk sac, fetal GI tract, and fetal liver
When is the Quad Screen ordered and what conditions is it screening for?
2nd trimester
Downs, trisomy 18, ONTD
What pattern on the Quad Screen is indicative of Downs?
b-HCG = high
uE3 = low
Inhibin-A = high
AFP = low
What pattern on the Quad Screen is indicative of trisomy 18?
b-HCG = low
uE3 = low
AFP = low
Other than ONTD, what can abnormal AFP levels be indicative of?
anencephaly
Why is accurate gestational dating so important?
So that the lab knows which levels of analytes to expect for comparison, otherwise results are not reliable.
Which conditions are associated with very low levels of uE3?
- Smith-Lemli-Opitz syndrome (SLO)
- steroidsulfatase deficiency (X-linked ichthyosis).
Usually discussed only when the MoM is < 0.3
this was on the midterm
Increased AFP can be associated with what condition other than ONTD?
ventral wall defects
Can see MoM values >7
In the setting of a normal ultrasound, what can be an explanation for increased AFP?
Bleeding in pregnancy
What is associated with very high levels of AFP? (MoM > 10)
congenital Finnish nephrosis
MoM is usually more like 20-30
