Prenatal Screening Flashcards
“identifying a small group of individuals from a large group to offer a more specific test”
Screening
Sensitivity is:
the number of people w/ a positive test divided by number of people the the disease
Specificity is:
of people with negative test and don’t have the disease divided by people who don’t have the disease
A screen’s detection rate =
% of people with disease that the screen will idnetify
The screen positive rate is:
% of population that screens positive
False positive rate:
proportion of individuals with a positive screen that are actually unaffected
The screen positive rate includes:
includes true and false positives
What is the negative predictive value (NPV)?
probability that someone with a negative screening test actually does not have the condition
What is the positive predictive value (PPV)?
probability that someone with a positive screening test will truly have the condition
Are PPV and NPV static?
No, they depend on how high a person’s initial risk was.
PPV for a women that’s 35 and screen positive for t21 going to be much higher than 20yo women with screen positive result
What is MoM? What is it important?
multiple of the median
allows us to compare to the median value for race, ethnicity, gestational age, etc.
AMA is considered:
women over the age of 35
When is 1st trimester screening completed?
btwn 11-13wks
What analytes are evaluated in first trimester screens? What other measurement is taken?
PAPP-A
hCG
nuchal translucency
What crown rump length is ideal for NT measurement?
45-84mm
What effect does maternal BMI have on analytes?
all concentrations are decreased
What sorts of causes do we see with increased NT?
50% t21 25% trisomy 13 or 18 10% turner syndrome 5% triploidy 10% other
When does the Quad screen typically occur?
15-22wks
What proteins are analyzed in the Quad screen?
AFP
hCG
Inhibin A
uE3
What produces AFP? When does it peak? What is considered elevated?
yolk sac then GI tract and liver of fetus
peaks from wk 10-13 (maternal leves peak in 3rd trimester)
> 2.5MoM
What produces hCG? When does it peak?
produced by syncytiotrophblasts
increases rapidly in 1st 8wks, decreases through wk20 then levels off
Which analyte is the most sensitive marker of Down syndrome?
hCG
detects 25-50% if used alone
What produces uE3? When does it peak?
What conditions is it seen with?
produced by the placenta
steadily increases throughout pregnancy
very low levels in SLO and X-linked ichthyosis
What produces Inhibin A?
gonads, corpus luteum, decidua, and placenta
What trend do we see on a Quad screen for a pregnancy affected by Down syndrome?
low AFP
low uE3
high hCG
high Inhibin A
What demographic is absolutely critical when screening?
gestational age/ estimated due date
When would we recalculate a quad screen result?
if date is off by 10-14 days
What is integrated screening?
1st trimester NT and PAPP-A
then 2nd trimester Quad screen -> report
What is studied in NIPS?
cell-free DNA
Where does cfDNA come from?
results from apoptosis
roughly 10% is placental
cfDNA requires a certain % of placental DNA. This is known as the ______. What % is ideal?
fetal fraction
10%
what happens if the fetal fraction is too low?
there is a no-call result
those individuals have an increased risk of abnormalities
What are the current detection and false positive rates of T21, 13, 18, and monosomy X using cfDNA?
T21: 99.7% DR, ;0.04% FPR
t18: 97.9% DR, 0.04% FPR
t13: 99% DR, 0.04% FPR
Monosomy X: 95.8% DR, 0.14% FPR
What are the primary methods of invasive prenatal dx?
CVS
amniocentesis
When is amniocentesis performed?
16-20wks
What risks are associated with aminocentesis?
1:300-1:500 chance for miscarriage
leakage of amnio. fluid, infection, fetal injury by needle
What are potential causes of high AFP?
contamination, fetal death, multiple gestations, ventral wall defects, nephrosis, miscalculation of GA
When is CVS performed? What is sampled?
10-13wks
chorionic villi that originate from trophoblasts (should match fetus DNA)
What methods of PGD exist?
blastomere biopsy
blastocyst bopsy
What protein trends do we see in Trisomy 21 in 1st and 2nd trimester?
1st: increased NT, decreased PAPP-A, increase hCG
2nd: decreased uE3, decreased AFP, increased Inhibin A, increased hCG
What protein trends do we see in Trisomy 18 in 1st and 2nd trimester?
1st: increased NT, decreased PAPP-A, decreased hCG
2nd: decrease uE3, AFP, and hCG; no change to Inhibin A
What protein trends do we see in Trisomy 13 in 1st and 2nd trimester?
1st: increase NT, decreased PAPP-A and hCG
2nd: 2nd: decrease uE3, AFP, and hCG; no change to Inhibin A
What protein trends do we see in a NTD in 1st and 2nd trimester?
1st: no change
2nd: highly elevated AFP
What level of testing should be offered to all prenatal patient?
screening and diagnostic testing
What are the limitations seen with Integrated screening?
test results are later along in pregnancy
significant drop out (often due to lack of 2nd blood draw)
Embryonic age begins:
at the point of conception (38wk is full term)
Why is full term in gestational age 40 wks vs. 38wks?
Dated from LMP (includes two weeks before conception)
Antepartum =
prenatal period
Intrapartum =
period of time during labor and delivery
Peripartum =
last month of gestation and first few months after delivery
What is the time range of the 1st trimester?
0w1d through 13w6d
What is the time range of the 2nd trimester?
14w0d through 27w6d
What is the time range of the 3rd trimester?
28w0d through end of pregnancy 42w0d
What the first period of development?
Germinal: fertilized egg -> implanted blastocyst (end of week 2)
What is the second period of development? What vital process occurs in this period?
embryonic (3rdwk-8/10th wk gestation)
Gastrulation and neural tube formation occurs
creation of germ cell layers and neural tube
What is the third period of development? What vital process occurs in this period?
Fetal (9/11wk-end of pregnancy)
organogenesis occurs in this period
When are embryos typically transferred in IVF? Why is this helpful?
3-5 days after fertilization
allows us to determine gestational age (2w3d-2w5d)
How often are women seen during pregnancy?
every 4wks from beginning to wk28
every 2wks btwn 38-36wks
every wk from 36 to delivery
Gestational diabetes can be associated with what outcomes?
preeclampsia, C-section, respiratory distress
What is the purpose of 1st trimester ultrasound?
determine viability and accurately date
may help determine chronicity if multiple gestations
When and why are 2nd trimester ultrasounds performed?
ideally 18-20wks
used to eval anatomy (“anatomy scan”)
What is the purpose of 3rd trimester US?
re. eval fetal anatomy
may also check fetal growth, well-being, amniotic fluid levels, and fetal position for delivery
Gravida means:
woman who is pregnant
Gravidity is:
total # of confirmed pregnancies, regardless of outcome.
Parity is divided into ___ sections. They are:
4
Term
Preterm
Abortion
Living children
Term pregnancies are considered:
live or stillbirth @ 37w0d or later
Preterm pregnancies are considered:
live or stillbirth btwn 20w0d-36w6d
Abortions (in pregnancy hx) are considered:
SAB, elective termination, and ectopic preg. 19w6d or earlier
Living children includes:
all living, twins and multi. count individual here unlike others
this doesn’t include adopted children
a test with 90% sensitivity would identify:
90% of people with the condition
The higher the specificity, the less likely you are to get:
a false positive
How do we describe clinical utility?
how useful a test is in determining/changing clinical management of the pt completing the test
What analyte pattern might you expect with intrauterine growth restriction?
high AFP, inhibin A, and hCg in 2nd trimester
What analyte pattern might you expect in a spontaneous miscarriage?
very low hCG in 1st trimester
what analytes might you expect in confined placental mosaicism trisomy 16?
high AFP and hCG in second trimester
What would low AFP in the second trimester lead you to believe?
preterm birth, stillbirth, miscarriage
What outcome is consisten with a cystic hygroma? in first trimester? second?
what other conditions are high on the differential w/ cystic hygroma?
aneuploidy
1st: Down syndrome
2nd: Turner syndrome
other: Noonan syndrome
If a pt elects cfDNA testing, what should you also offer and why?
2nd trimester AFP
look for OTND because cfDNA doesn’t look for hormone/protein levels
When can CVS be performed in 2nd trimester?
to evaluate for oligohydramnios
Why isn’t CVS recommended before 9-10wks?
risk of limb reduction
What are some of the limitations of CVS?
confined placental mosaicism
maternal cell contamination
What is a common cause of confined placental mosaicism? What may be a reflex?
trisomy rescue
follow up fro potential UPD
Why would a pt be given RhoGAM? Why?
if they are Rh-
prevent alloimmunization
