OBGYN Labs & Diagnostics Flashcards
Describe the difference between urine hCG and serum hCG
Which hCG test measures beta human chorionic gonadotropin
serum
Describe the levels of hCG over the first 8 weeks of pregnancy
hCG doubles every 1.5-2 days for the firs 8 weeks
Describe instances of a false negative on a urine pregnancy test
- early pregnancy
- very high hCG (hook effect)
Describe instances of a false positive on a urine pregnancy test
- heterophile antibodies (mono)
- menopause (hCG secretion by pituitary)
Describe the indications for a serum (quant) hCG
- amenorrhea
- early pregnancy
- bleeding/abd pain in early pregnancy (ectopic pregnancies will not show hCG doubling as it should, spontaneous abortions will show a decreasing or improperly rising hCG)
- monitoring after ectopic, miscarriage, gestational trophoblastic disease
- hCG secreting tumors
Describe hCG levels in an ectopic pregnancy
Do not double as it should (1.5-2 days for 8 weeks)
Describe the components of a first trimester screen
(Trisomy 21, 18, 13)
at 10-14 weeks
Blood
- hCG
- pregnancy associated plasma protein A: protein from placenta
Ultrasound measurement of nuchal translucency for aneuploidy
THEN do a serum Alpha fetoprotein (neural tube defects) at 15-22 weeks
Describe the components of a quad screen
(Trisomy 21, 18, 13, neural tube defects)
15-22 weeks
Blood tests only
- hCG
- estriol: predominant
- inhibin A: secreted by ovaries & placenta
- serum AFP: neural tube defects
Describe the differences in quad screening between Trisomy 21 and Trisomy 18
Trisomy 21
- hCG elevated
- estriol decreased
- inhibin increased
- AFP decreased
Trisomy 18
- all decreased
What can you determine from first trimester screening & quad screening
- gestational age
- maternal weight
- number of fetuses
- DM
Potential causes of abnormal results: incorrect dating, presence of twins, fetal demise
Describe the indications for fetal anomaly screening
- all pregnant patients (FTS or quad screen)
- high risk patients: sequential screen (FTS AND quad screen)
- if abnormal: cell free fetal DNA, chorionic villus sampling, amniocentesis
Describe cell-free fetal DNA testing
- maternal blood sample (10+ weeks gestation) DNA fragments amplified & sequenced
- Trisomies will have a higher % of DNA fragments from the extra chromosome
- very low false positive rate
- Tests for trisomies & Turner syndrome (monosomy X)
Describe the indications for fetal DNA based screening
- pregnant patients at risk of fetal aneuploidy (AMA, abnormal fetal US, previous aneuploidy, abnormal screen)
- offer neural tube ultrasound and/or AFP for neural tube defects
Describe chorionic villus sampling
- sample of chorionic villi removed from placenta via transcervical/transabdominal collection
- 11-14 weeks gestation
- slight risk of miscarriage, Rh sensitization, infection
- offer neural tube ultrasound and/or AFP for neural tube defects
- indicated after positive screen & diagnoses trisomies or other genetic conditions (CF)
Describe amniocentesis fetal anomaly testing
- sample of amniotic fluid transabdominally
- 15-20 weeks
- indications: genetic testing, fetal lung maturity, fetal infection/hemolytic disease, paternity testing
- Risks: miscarriage, Rh sensitization, infection, amniotic fluid leak, needle injury
Describe optional carrier screening
- screens for 175+ genetic conditions
- best done prior to conception, can be done during pregnancy
- can test one or both partners
Describe the routine tests in pregnancy at first prenatal visit (10-12 weeks)
- Blood type & antibody screen (assess risk of hemolytic disease of the newborn)
- CBC
- RPR or treponemal syphilis test
- Hep B surface antigen
- HIV antibody (false positives)
- Rubella antibody (vaccine after delivery if non-immune or equivocal)
- GC/CT testing (treat if +)
- urine culture (treat if asymptomatic bacteriuria)
Describe the routine tests in pregnancy at 24-28 weeks
- 1 hr oral glucose tolerance test with reflex to 3 hour fasting if abnormal (for gestational DM)
- Hgb and/or CBC (for anemia)
Describe the routine tests in pregnancy done at around 36 weeks
- group B strep culture (swab vagina AND rectum: give abx during labor if positive)
Describe what a urine dip at a prenatal visit can tell us
Check for proteinuria & glucosuria
- protein: concern for preeclampsia (along with elevated BP)
- glucose: concern for gestational DM
Describe testing done in recurrent pregnancy loss
- karyotype (parental & fetal tissue if possible)
- LH, FSH, TSH, PRL, cortisol (endo abnormalities)
- thrombophilia panel: protein C & S, antithrombin, Factor V Leiden, prothrombin gene mutation, lupus antigoaculant, anticardiolipin Abs
- ANtithyroid Abs
- Test for DM (glucose, Hgb A1C)
Describe when/why a CBC is checked in pregnancy
- routine screening in early pregnancy
- second trimester anemia check
- symptoms of anemia
- pregnancy complications
- HELLP syndrome (hemolysis, low PLT, also get peripheral blood smear)
Describe why a CBC is checked in gyn presentations
symptoms of anemia & menstrual abnormalities (menorrhagia)
Describe the indications for liver enzyme testing in pregnancy
- fatty liver of pregnancy: mild liver enzyme elevation (abnormal coag tests, rarely results in acute liver failure)
- HELLP syndrome: elevated liver enzymes
Describe the labs for preterm labor testing
Fetal fibronectin test
- indicated in pts with sxs of preterm labor
- 22-35 weeks
- vaginal swab
- HIGH NEGATIVE PREDICTIVE VALUE
(protein produced at boundary between amniotic sac & uterus)
Why would we check bile salts in late pregnancy
testing for cholestasis of pregnancy (itching!)
- blood test