USMLE Step 3 OBGYN Notes


  • Management of HSV in pregnancy:
    • History of HSV infection?
      • If yes, then give antiretroviral Tx (acyclovir) starting at 36 weeks gestation until delivery;
    • if active lesions peripartum then do C-­‐section;
    • if no active lesions peripartum then vaginal delivery is appropriate.
    • If no history of HSV infection, then has there been exposure to an HSV-­‐infected partner?
      • If no, no further testing is necessary.
      • If yes, then HSV serology (IgG antibody screen) is done. 
        • If (-), no further testing.
        • If (+), then give acyclovir starting at 36 weeks.
  • Kidney donation increases the risk of gestational complications (i.e., fetal loss, preeclampsia, gestational diabetes, gestational hypertension). These risks are increased in the patient only, not relative to the general population, meaning women should generally attempt to complete childbearing before kidney donation, although non-­‐completed childbearing is not a contraindication to donation. There is no increased risk of mortality, end-­‐stage renal disease, or depression.
  • The risk of a subsequent pregnancy with Turner syndrome after having a child with 45XO is the same as the general population. And maternal age also does not increase the risk of a baby with Turner.
  • HAART is two NRTIs + either 1 NNRTI or protease inhibitor. Efavirenz is associated with neural tube defects, facial clefts, and anophthalmia prior to 8 weeks gestation. However, if a woman is already on efavirenz and has effective viral control (<50/mL), the drug should NOT be switched because of the risk of drug resistance and viral failure (>50/mL after 24 weeks on HAART) outweigh the risk of teratogenicity. So any drug regimen the mom is on during pregnancy, even if it includes efavirenz, should be maintained throughout
  • If a woman is not on HAART during pregnancy, she should be given intrapartum zidovudine + have a C-­‐section, then start HAART after parturition.
  • The neonate of HIV(+) mom should receive zidovudine for 6 weeks + serial HIV PCR testing.
  • A c-­section should be performed if viral load >1000 copies/mL, as the risk of transmission. transmission is ~2% with C-­‐ The risk of transmission is also ~2% with vaginal delivery if the mom has an undetectable viral load (>50).
  • Avoid instrumentation (e.g., vacuum, forceps), fetal scalp electrode, and artificial rupture of membranes (ROM) during parturition in HIV(+) women.
  • Avoid amniocentesis unless the viral load is undetectable.
  • Nevirapine is associated with life-­‐threatening hypersensitivity in patients with CD4 counts >250.
  • Bishop scoring is a pre-­labor scoring to determine whether induction of labor will be required.
    • Bishop scoring = PCFED = cervical Position, cervical Consistency, Fetal station, cervical Effacement, cervical Dilation.
    • The highest score is 13;
    • Score 5 or less = labor unlikely to start without induction;
    • Score 9 or greater = labor likely to happen spontaneously.
    • Components:
      • Position: posterior 0 points, middle 1 point, anterior 2 points Consistency: firm 0 points, medium 1 point, soft 2 points
      • Fetal station: -­3 station relative to ischial spines as reference point (~3-­‐4 cm inside vagina = 0 points; -­‐2 station = 1 point; 0/+1 = 2 points; +2/+3 = 3 points
      • Effacement: refers to how ‘thin’ the cervix is; cervix is normally 3cm long; as it prepares for labor it thins; 0-­‐30% = 0 points; 40-­‐50% = 1 point; 60-­‐70% = 2 points; 80+% = 3 points
      • Dilation: closed 0 points, 1-­‐2cm = 1 point; 3-­‐4 cm = 2 points; 5+ cm = 3 points
  • Thyroid screening during pregnancy is initially done with just TSH (trimester-­‐specific ranges) +/-­‐ total T4. Also important to know that the levothyroxine dose needs to be increased by 25-­50%, especially during the first trimester, to meet increased metabolic demands.  Initially, b-­‐hCG binds to TSH receptor and can increase T3/T4 and decrease TSH, but increasing estrogen levels increase TBG levels and increase total T4 by ~1.5x. Free T4 is not reliable and tends to be artificially low due to assay artifact. Serum T3 is not useful in the management of hypothyroid patients, including those who are pregnant and are not a sensitive marker of thyroid status. T3 levels often remain normal despite under-­‐replacement of thyroid hormone.
  • Indications for C-­section in twin pregnancy are monochorionic-­‐monoamniotic twins; if presenting (first) twin is in breech position; if non-­‐presenting (second) twin in either vaginal or breech position is <1500g or >20% the estimated weight of the presenting twin; if either twin has non-­‐reassuring HR monitoring.
  • Acyclovir should be given starting 36 weeks gestation in pregnant women with HSV. Only do C-­‐section if there are peripartum prodromal Sx or active lesions. C-­‐section decreases transmission risk from 7% to 1.2% in these cases.