OB Lab Med Flashcards
Qualitative betahCG
- urine ELISA test for b-hCG
- home tests often NOT as sensitive as advertised
- threshold: 10-100 mIU/ml (only 44% of brands are positive at 100)
quantitative beta-hCG
- serum ELISA for b-hCG
- detectable as low as 1 mIU/ml threshold
what determines if a home pregnancy test is valid or not?
- the control has to be positive for the test to be positive
- a positive or negative test with no control is INVALID
trend of hCG when looking at quantitative hCG testing
-per the book: doubles q 48-72 hours - but be conservative***
when does hCG peak?
between 8-11 weeks
when can transvaginal US usually find a gestational sac? (in terms of hCG levels)
> 1000-2000 mIU/ml
what could cause hCG levels to be too high?
- incorrect dates (MC)
- twins
- molar pregnancy
- Down syndrome
what could cause hCG levels to be too low?
- incorrect dates
- Trisomy 18
- ectopic pregnancy (50%)
what is the discriminatory zone?
- 1500-2000 mIU/ml
- if level is above the zone threshold, but cannot see IUP on TVS –> either non living or ectopic (possibly multiples)
yolk sac
- what is it
- when is it seen
- circular, 3-5 mm diameter structure
- typically seen w/i the gestational sac at about 5/5 weeks
- should see embryo at 6 weeks and cardiac activity at 6.5 weeks
what does it mean when there is no IUP on TVS? and what is the next step?
= PUL (pregnancy of undetermined location)
-repeat hCG in 48 hrs
outcome of failure of hCG to rise as expected or a drop?
failing IUP or failing ectopic
-after SA, levels decline by 20-35% at 48hrs and 70-85% by 7 days
outcome of a rise of hCG but still no gestational sac on TVS?
ectopic
outcome of a rise of hCG and you see the gestational sac?
WHEW! IUP
summary of what is expected in serial hCG levels
- early normal IUPs have about 50% rise at 48 hrs (it might double and that’s ok)
- be conservative! Some nl IUPs have only a 35% rise at 48 hrs
what trend in hCG do you expect w/ multiples?
the same rate of rise as a nl IUP
what to keep in mind with serial hCG and ectopics
- 30% of ectopics will have about a 50% rise at 48 hrs (like nl IUP)
- an ectopic w/ declining hCG levels can still rupture!! (50%)
what progesterone level EXCLUDES ectopic?
-progesterone > 25 ng/ml (92% sens.)
what is progesterone levels in most ectopic pregnancies?
10-25 ng/mL
progesterone levels < 5 ng/mL could mean what?
- non-living IUP
- ectopic
What are the standard initial labs for a pregnant pt?
- blood type
- D(Rh) type
- antibody screen
- CBC
- PAP
- confirm immunity to rubella
- VDRL (syphilis)
- UA
- HBsAg
- confirm no abs to HIV
- GTT if hx of gDM
optional labs to run for pregnant pt
- electrophoresis (for bleeding disorders)
- PPD (TB screen)
- G/C: chlamydia for all, G if RFs
what is Rh incompatibility
- dad is Rh +
- Rh+ fetal blood exchanged antenatal or at delivery
- Rh- mom make Rh Rho(D) abs once exposed
- 1st child unaffected
- subsequent kids at risk for hemolytic anemia
who gets RhoGAM?
every Rh - mom, no matter what
what is the TORCH panel?
T: toxoplasmosis gondii O: other (including syphilis) R: rubella C: cytomegalovirus H: herpes simplex virus
complications of rubella infection in utero
- stillbirth
- miscarriage
- congenital rubella syndrome: birth defects including heart problems, microcephaly, vision/hearing probs, intellectual disability, growth probs, and liver/spleen damage
GTT
- screen for gestational DM
- give 50mg glucose and draw blood in 1 hr
- nl: < 140 mg/dl*** (know this)
- if abnl, do 3 hr test w/ 100 g challenge
RhoGAM injection
-at 28 weeks if mom is Rh - or w/i 72 hrs postpartum
what is RhoGAM
IgG anti-Rho(D) antibody that binds to Rh+ cells, makes the “invisible” to maternal immune system
RFs for impaired carb metabolism in pregnancy
- strong fam hx of DM
- prior delivery of a large newborn
- persistent glucosuria
- unexplained fetal losses
abnl results of a 3 hr GTT (per ADA)
- fasting: >95
- 1 hr: >180
- 2 hr: >155
- 3 hr: >140
maternal serum alpha fetoprotein (MSAFP) should be offered to who?
EVERYONE
MSAFP
- when to get
- what is it
- obtained b/w 14-22 weeks but most accurate 16-18 weeks
- a screening test for birth defects/ chromosomal abnormalities
indications for MSAFP
- personal or fam hx of birth defects
- > 35
- DM I
- used harmful meds during pregnancy
risk of chromosomal anomaly by maternal age
- 20 yo: 1/525
- 40 yo: 1/62
- 45: 1/18
when is an instance other than birth defect that MSAFP could be elevated?
liver carcinoma
MSAFP
- how is it measured
- specificity
- measured in MOMs; allows for comparison of results based on pt. population
- poor specificity: if abnl, only 2-3/100 will have a birth defect (just tells you to go looking, not diagnostic)
what to do if MSAFP is abnl
- send for US
- repeat lab
- amniocentesis
- genetic counseling
- and/or special testing
MSAFP is high in:
- NTDs
- esophageal probs
- omphalocele
- gastroschisis
- placental abruption
- multiple gestation
- liver dz in the mom
- inaccurate gestational dating***** MC!
MSAFP is low in:
- Trisomy 21 (Down syndrome)
- Trisomy 18 (edward’s)
- other chromosomal abnormalities
- insulin dependent diabetics
- very low sensitivity
what tests make up the triple screen?
- AFP
- UE3 (estriol)
- hCG
triple screen
- when is it best?
- sensitvity
- best b/w 16-18 weeks
- 70% senstivity, 5% false +
what results are expected in the triple screen in Trisomy 21?
- AFP: low
- UE3: low
- hCG: high
what results are expected in the triple screen in Trisomy 18?
- AFP: low
- UE3: low
- hCG: low
what results are expected in the triple screen in NTDs, abd wall defects, etc.?
- AFP: high
- UE3: NA
- hCG: NA
What tests make up the quad screen?
- AFP
- UE3
- hCG
- DIA (inhibin A)
quad screen
- when is it best?
- sensitivity
- best b/w 16-18 weeks
- 80% sensitivity, 5% false +
Tri 21 quad screen
- AFP: low
- UE3: low
- hCG: high
- DIA: high
Tri 18 quad screen
- AFP: low
- UE3: low
- hCG: low
- DIA: normal
Tri 13 quad screen
- AFP: high
- UE3: nl
- hCG: nl
- DIA: nl
Turner’s syndrome quad screen
- AFP: low
- UE3: low
- hCG: very high
- DIA: very high
NTDs, abd wall defects, etc. quad screen
- AFP: high
- UE3: NA
- hCG: NA
- DIA: NA
materniT21
- Tests maternal blood for fetal chromosome 21 • Screening test
- Pros: Can be done as early as 9-10 weeks, high sensitivity and specificity, non-invasive • Cons: Not diagnostic (still need CVS or amnio), $$$, only tests for Trisomy 21
M aterniT21 PLUS
- detects chromosomal abnormalities: Tri 21, 18, 13
- Gender
- sex aneuploidies: Turner’s, Klinefelters
- selected microdeletions: DiGeorges, Prader willi, Cri du chat
indications for MaterniT21
- Advanced maternal age
- Personal hx of chromosomal abnormalities
- Family hx of chromosomal abnormalities or birth defects
- Fetal US abnormality suggestive of chromosomal abnormalities
- Positive screening test
what is chorionic villus sampling (CVS)?
- uses US to aspirate chorionic villi from placenta
- to detect chromosome abnormalities
- transcervical or transabdominal
- only paternity test prior to delivery
- can be preformed at 10-14 weeks
indications for CVS
- AMA
- abnl screening test
- fam hx
benefits of CVS over amnio
- can be done earlier
- larger samples
- faster results (but higher risks)
risks of doing CVS
- miscarriage (1-5%)
- infection
- distal limb defects
- premature rupture of membranes
what is amniocentesis
- US guided transabdominal aspiration of amniotic fluid (contains fetal cells)
- done after 15 weeks to assess for chromosomal abnormalities or gender
what is amniocentesis used for in the 3rd trimester?
- fetal lung maturity
- infection
- hemolytic incompatibility
indications for amniocentesis
- AMA, >35 yo
- prior pregnancies w/ birth defects
- abnl blood tests or US
- fam hx of genetic disorder
risks of amniocentesis
- miscarriage (less than CVS)
- PTL
- chorioamnionitis
cordocentesis
- done after 17 weeks
- US guided, transabdominal aspiration of fetal blood from umbilical cord
- last resort!
- to detect chromosome abnormalities, blood disorders, infection
risks of cordocentesis
- miscarriage (1-2%)
- bleeding
- infection
- PROM
- fetal bradycardia
lab testing in 3rd trimester
- repeat CBC
- if sexual RFs, check STIs again after 32 weeks
- consider US if indicated
- EVERYONE get group B strep swab
group B strep swab
- b/w 35-37 weeks
- swab of vagina and anus
- about 10-25% of women are colonized
- helps prevent infection in newborns
- # 1 infectious cause of morbidity/mortality among infants in the US
