Testing Options Flashcards
What is the timing of a first trimester screen and what is it used for?
10-13w6d; For T13, T18, and T21
What is included in the first trimester screen?
NT measurement, PAPP-A, hCG measurements
What is PAPP-A
protein produced by the growing placenta and increases until delivery
What is hCG
hormone produced by the placenta in large quantities. Levels rapidly rise for the first 8-10 weeks then decrease and stabilize for the remainder of the pregnancy
What is the hCG trend for T13 and T18
Decreased
What is the hCG trend for T21
Increased
What is the hCG trend for triploidy/molar pregnancy
Extremely increased
What is the NT measurement
Increased fluid in the back of the baby’s neck; above the 95th percentile (3.0mm)= increases the possibility of an aneuploidy; greater than or equal to 3.5mm is above the 99th percentile and could also mean a cardiac defect
What are the cutoff values of a first trimester screen based off of
Selected based off of a less than or equal to 5% false positive rate (for T21 screen positive it is greater than or equal to 1 in 230; for T18 screen positive it is greater than or equal to 1 in 100)
What are the advantages and disadvantages of the first trimester screen
Advantages: 1st tri results, 1 visit, CVS available if +, incorporates maternal factors: age, prior aneuploidy, weight, race, # of fetuses
Disadvantages: lower detection rate compared to integrated screen (~85% for T21), false + could be due to incorrect dating
What population is first trimester screen usually offered to
If a physician with an early to care pop has access to and NT provider and CVS and prefers to complete screening in one visit
What are the trends in a first trimester screen that would indicate T21
Increased NT, decreased PAPP-A, increased hCG
What are the trends in a first trimester screen that would indicate T18
Increased NT, decreased PAPP-A, decreased hCG
Everything DownWARD (Edward, Everything Low)
What are the trends in a first trimester screen that would indicate T13
Increased NT, decreased PAPP-A, decreased hCG
When the NT is high, what biochemical marker is always low
PAPP-A
What is the timing of a second trimester screen and what is it used for?
Timing is 15-21w6d; For ONTDs, T18, T21, T13 (sometimes)
What is included in the second trimester screen?
AFP, hCG, uE3, Inhibin A
Three types: QUAD screen, Integrated MSS, Sequential MSS
What is AFP
Protein produced by the fetal tissue and rises until the 12th wk then gradually falls until birth. If there are problems with the baby, AFP crosses the placenta into mom’s blood (which originated in the amniotic fluid)
What is the detection rate for ONTDs using AFP
85%
What can cause elevations in AFP
GA younger than calculated, spina bifida/anencephaly, pilonidal cysts, AWDs, liver necrosis, GI obstruction, cystic hygroma, urinary obstruction, polycystic kidney, absent kidney, congenital nephrosis, OI, low birth weight, oligohydramnios, multiple gestation, low maternal weight
What can cause low levels of AFP
GA older than expected, trisomies, hydatiform mole, fetal demise, high maternal weight
What can effect hCG levels?
maternal weight, parity
>3.5MoM= poor fetal outcome
What is uE3
form of estrogen produced by fetal metabolism, which involves the liver, adrenals, and placenta. Some crosses the placenta. Levels rise until ~8th week and continue to increase shortly before delivery
What is very low uE3 (<0.15MoM) and indicator of?
SLO or X-linked ichthyosis (Steroid sulfatase deficiency)
If you cannot produce enough cholesterol (like the conditions above), you cannot produce estrogen or testosterone (both will be decreased on NBS)
What is the QUAD screen?
Does not include the NT measurement and does NOT assess risk for T13
Low analyte levels can also be associated with placental insufficency
Incorporates factors like age, weight, race, DM
Inhibin A increases the detection rate for DS
What is the ideal timing for ONTD screening
16-18wks
What is a PENTA screen
Incorporates invasive trophoblast antigen (ITA); Detection rates are not substantially increase over QUAD
What is the integrated MSS?
Two step process to adjust the maternal age- related risk for DS and T18. Pt is given a single RA after 1st tri screening and QUAD screening
Detection rate for T21 is 94-96% and T18 is 91-96%
Eliminates the possibility of CVS
What is the stepwise sequential MSS?
Combines 1st tri screen and maternal age, then are grouped into high or low risk categories. High risk is offered dx testing, low risk group moves onto QUAD screen
Detection rate for T21 is 94-96% and T18 is 91-96%
What are the trends in a second trimester screen that would indicate T21
Decreased AFP, Decreased uE3, increased hCG, increased Inhibin A (only detects T21)
What are the trends in a second trimester screen that would indicate T18
Decreased AFP, decreased uE3, decreased hCG
Everything DownWARD (Edward, Everything Low)
What are the trends in a second trimester screen that would indicate T13
Decreased hCG
What are the trends in a second trimester screen that would indicate ONTDs
Very high AFP
What is inhibin A
hormone produced by the placenta that decreases slightly from 14-17wks GA then rise again
ONLY DETECTS T21