pregnancy tests Flashcards
prenatal care of 1st trimester
patients should be seen every 4-6 wks:
- 11-14 wks: US to confirm gestational age + check nuchal translucency
- fetal heart sound at the end of the trimester
- blood tests, pap tests, pap smear, gonor/chl tests
- 1st trimester screening may be offered
what is 1st trimester screening
noninvasive evaluation to identify risks of ch abnormalities –> it is a combination of blood tests + US that evaluates the fetus for possible Down syndrome
what is 2nd trimester screening
- screen for genetic + congenital problems (triple or quad screen at 15-20 wks
- auscultation of fetal heart rate
- 16-20 wks: quickening (feelling fetal movement for the first time) - multiparous women earlier
- 18-20 wks routine US for fetal malformation
triple vs quad screen
triple: maternal serum alpha fetoprotein (MSAFP), β-MCG, estriol.
quad: adds inhibin A
increase in MSAFP may indicate … / how to increase the sensitivity of the test
- dating error
- neutral tude defect
- abd wall defect
The addition of beta-HCG estriol and inhibin A helps increase the sensitivity of MSAFP test
what is 3rd trimester screening
- visits are every 2-3 wks until 36 wks
- after 36 wks, visit every week
- blood count at 27 wks
- glucose load at 24-28
- test for microorganisms in 36 wks
third trimester testing - complete blood count
27 wks: if Hb under 11 –> iron orally (with stool softeners)
third trimester testing - test for microorganisms
36 wks: Cervical culture for Chlamydia + gonorrhea –> treatment if positive
rectovagina culture for group B strep -> prophylactic antibiotic during labor
other screening test - types
- Chorionic villus test
- amniocentesis
- fetal blood sampling
Chorionic villus test - when and indications
at 10-13 wks in:
- advance maternal age
- known genetic disease in parent
Chorionic villus test - technique / purpose
catheter into intrauterine cavity to aspirate chorionic villi from placenta (tranabdominally or transvaginally) –> obtains fetal karyotype
amniocentesis - when and indications
after 11-14 wk:
- advance maternal age
- known genetic disease in parent
amniocentesis - technique / purpose
needle transabdominally into the amniotic sac and withdraw amnitoci fluid –> obtains fetal karyotype
fetal blood sampling - indications
done in patients with Rh isoimmunization and where a fetal CBC is needed
fetal blood sampling - technique / purpose
needle tranabdominally into the uterus to get blood from the umbilical cord –> percutaneous umbilical blood sample
mother screening for Rh incompatibility
Rh antibody screening (during 1st prenatal visit)
- –> no further screening
- Rh (-) –> antibody titer
a. if sensitized (have antibodies)–> further monitor
b. if unsensitized (no antibodies) –> repeat at 28 wks and if still (-) give Rhogam (anti-D) as indicated
- At delivery: if newborn is Rh (+) –> again Rhogam to mother
hemolytic disease of newborn - presentation and mechanism
- fetal anemia –> extramedullaty RBCs production (liver + spleen)
- hemolysis –> increased heme + bilirubin (neurotoxic)
- high fetal cardiac output
some scenarios where fetal blood cells may cross into the mother’s blood (sensitising the mother)
- amniocentesis
- abortion
- vaginal bleeding
- placental abruption
- delivery
further monitor in Rh (-) sensitized pregnant
antibody titer via indirect antiglobulin test:
- the patient is consedered sensitized if she has a titer level more than 1:4
- if less than 1:16 –> no further treatment / but if reaches 1:16 at any point during pregnancy, serial amniocentesis should be done (evaluation of fetal bilirubin level)
pregnant’s antibody titer for Rh equals or more than 1:16
–> ….
do 1st amnioncentiesis at 16-20 wks:
- fetal cells Rh (-) –> manage like normal pregnancy
- Rh (+) –> amniocentesis evaluated under spectrophotometer (to evaluate bilirubin):
a. low bilirubin –> repeat amniocentesis in 2-3 wks
b. medium –> repeat in 1-2 wks
c. high –> fetus is anemic –> do percutaneus umbilical blood sample (for Hct) –> low Hct –> perform intrauterine transfusion
fetal testing after 32 weeks
- 32-36: weekly nonstress test (NST) for fetal well being and US (fetal size)
- more than 36: twice weekly testing: 1 NST and 1 biphysical profile (amount of amniotic fluid + fetal well being)
- 37 lecithin / sphingomyelin (assess lung maturity, if ok deliver)
- 38-39: no test / labor induction
Indications for prophylactic administration of anti-d immune globulin for Rh(D) negative patients
- at 28-32 weeks
- less than 72 h fter delivery of Rh (+) infant
- less than 72 hours after spontaneous abortion
- ectopic pregnancy
- threatened abortion
- hydatidiform mole
- chorionic villus sampling, amniocentesis
- 2nd + 3rd trimester bleeding
- external cephalic version (?)
karyotyping of fetal tissue after 1 spontaneois miscarrieage
not indicated –> considered after recurrent pregnancy or loss in the 2nd trimesterb
when to give anti-D (time) / dose
28 weeks and within 72 h of delivery
- a standard dose of anti-D immune globulin at 28 wks in uncomplicated pregnancy is adequate/ however if the patient developed placental abruption earlier in pregnancy, the Kleihauer-Betke test should performed to determine whether a higher dose is indicated for postpartum
when to check folate acid in pregnancy
not recommended
initial prenatal visit - labs
- Rh, antibodies
- Hb, MCV
- HIV, VDRL, HBsAg
- Rubella + varicella immunity
- Pap test
- Chlamydia PCR
- Urine culture
- Dipstick for urine protein
24-28 wks - labs
- Hb
- antibody screen if Rh (-)
- 50 g 1 hour
35-37 wks - labs
group B strep culture
increased nuchal translucency - next step
amniocentesis in 15 week
U/S assessment of gestational age - parameters
- Gestational sac diameter
- Crown-rump length
- Bi-parietal diameter, head circumference, femur length
U/S assessment of gestational age - parameters and accuracy in days
- Gestational sac diameter 4.5-6 (+/- 6 days)
- Crown-rump length 7-10 (+/-3 days) or 11-14 (+/-5 days)
- Bi-parietal diameter, head circumference, femur length 14-20 (+/- 7), 21-30 (+/-14), more than 30 (+/- 25)
trisomy 21 - quadruple screening
AFP: low
HCG: high
eastriol: low,
inhibin A: high
trisomy 18 - quadruple screening
AFP: low
HCG: low
estriol: low
inhibin A: normal/low
First trimester combined test - time / advantage / disadvantage
9-13 wks
- early screening
- not diagnostic
cell-free fetal DNA - time / advantage / disadvantage
more than 10 weeks
- high sens + specif for aneuploidy
- not diagnostic
chorionic villus sampling - time / advantage / disadvantage
10-13 wks
- definitive for karyotypic diagnosis
- invasive + risk for spontaneous abortion
2nd trimester quadruple screen - time / advantage / disadvantage
15-22 wks
- screens for neural tube defects + aneuploidy
- not diagnostic
amniocentesis - time / advantage / disadvantage
15-20
- definitive karyotypic diagnosis
- invasive, risk of membrane rupture, fetal injury, pregnancy loss
2nd trimester U/S - time / advantage / disadvantage
18-20
- Measures fetal growth, evaluates fetal anatomy, confirms placenta position
- cannot identify all abnormalities, some findings are of uncertain significance
