OB Prenatal Screening
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Who might benefit from genetic testing/counseling?
- Mother or father w/a genetic condition
- FH of genetic disease
- Previous child with: retardation, anomalies, dysmophic features
- AMA (adv mat age)
- at risk ethnic group
What are the main goals of prenatal genetic screening?
- Diagnose NTD
- (risk not affected by parental age)
- Identify fetuses with aneuploidy
- (risk increases with age)
When does the neural tube close?
What are some DS characteristics?
- Flat nasal bridge
- Small head with flattened occuput
- wide spaced eyes with epicanthal folds
- large tongue
- short stubby fingers and simian crease
ITA (Hyperglycosolated HCG)
Produced early (peaks at 9 wks)
↑ in DS, twins, Trisomy 22
↓ Trisomy 18, 13, preeclampsia
↓ levels :
- Trisomy 21
- Trisomy 18
- Trisomy 13
- Fetal demise
(Maternal serum Alpha Fetoprotein)
- High levels:
- NTD (anencephaly, spina bifida) abdominal wall defects
- High levels:
- Trisomy 21
- Twin gestation
UE3 (Unconjugated estriol)
Low levels ALL ABNORMAL
Inhibin A (Dimeric inhibin A)
High levels: Trisomy 21
Low levels: PCOS
What are MOM (multiples of the median)
Indicated how far a result is from the median of all pregnancies at that Gestational age
- 1.0 = NORMAL
- (risk is never reported as "zero")
When are MOMs adjusted
- by ethnic group
- for maternal weight
- if IDDM
What is a common reason for an abnormal MSAFP?
- Incorrect gestational age
- multifetal gestation
1st TM screening for Trisomy 21
- 1. Maternal Age
- 2. ITA
- 3. PAPP-A
- 4. Nuchal Translucency
2nd TM screening for Trisomy 21
- 1. AFP
- 2. HCG
- 3. Unconjugated estriol (uE3)
- 4. ITA or DIA
What is FNT (fetal nuchal translucency) used for and when is it done?
First trimester screening tool (12-13 wks) to identify
- Trisomy 18, 21
- Fetal Cardiac anomaly
Fetus compensates for delayed lymphatic connections by forcing excess drainage into nuchal area
What does the quad screen detect?
- Trisomy 21;
- HIGH: hCG and Inhibin ALOW: MSAFP & uE3
- Trisomy 18:
- LOW: AFP, HCG, ue3
What is the optimal time for CVS?
What happens with an "integrated approach" to screening?
NO ONE IS DIAGNOSED IN 1ST TM
- Everyone receives screening in 1st and 2nd TM
- No report given after 1st TM screen
- After 2nd TM a single result combining both values is reported.
- High risk (>1:270) gets amnio
Which screening option is the optimal approach?
What is the contingency approach?
- Act on results of 1st TM
- 1. High risk (>1:30) - - CVS
- 2. Intermediate (1:30 to 1:1500) 2nd TM Quad
- 3. Very low risk (1:1500), no further testing
75% only get 1st TM screening
Explain the Sequential Approach..
Bottom Line: 98% receive 2nd TM Quad screen
- Get 1st TM screen - - Act on results
- High risk (>1:30) - Offer CVS
- NL risk - 2nd TM Quad screen
- Combine results reported
- Amnio offered if risk >1:270
What is the next step after getting a POSITIVE test result?
Ensure the dates are correct.
Based on U/S or LMP
What test has the best Tri 21 detection rate?
Quad screen + genetic U/S
(90% detection rate)
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