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USMLE Step 3 - OB/GYN High-Yield Must-Knows

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1. PREECLAMPSIA / ECLAMPSIA / HELLP

• BP >= 140/90 mmHg on two occasions + proteinuria > 0.3 g/24 hr, after 20 weeks gestation
• Severe features: SBP > 160 or DBP > 110 + proteinuria > 5 g/24 hr + end-organ damage (headache, visual changes, RUQ/epigastric pain, oliguria < 500 mL/24 hr, pulmonary edema, thrombocytopenia, hemolysis, elevated LFTs)
• Edema alone is NOT a diagnostic criterion

• Mild: bed rest + close surveillance; delay delivery until fetal maturity or development of severe features
• Severe: deliver within 24 hours
• Seizure prophylaxis: IV Magnesium Sulfate - Loading dose 4 g IV over 15-20 min, then 2 g/hr maintenance. Continue 12-24 hours postpartum
• Acute severe HTN: IV hydralazine (first-line) if DBP persistently > 110 mmHg; labetalol IV or oral nifedipine also used
• Magnesium toxicity signs: loss of DTRs (first sign), respiratory depression, cardiac arrest. Antidote: calcium gluconate

• Hemolysis + Elevated Liver enzymes + Low Platelets
• Presents with RUQ/epigastric pain; may appear in seemingly stable patients
• Treatment: delivery (definitive); steroids may be given to mature fetal lungs or improve platelet count

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2. GESTATIONAL DIABETES (GDM)

• Screen all pregnant women at 24-28 weeks with 50 g glucose, 1-hr challenge (non-fasting)
• Abnormal if 1-hr glucose >= 140 mg/dL - follow with 100 g, 3-hr OGTT (fasting)
• GDM diagnosed if 2 or more values are abnormal on 3-hr OGTT:
  • Fasting >= 95-105 mg/dL
  • 1 hr >= 180-190 mg/dL
  • 2 hr >= 155-165 mg/dL
  • 3 hr >= 140-145 mg/dL

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3. ECTOPIC PREGNANCY

• Serial hCG levels 48 hrs apart - normal IUP doubles every 48 hrs; plateauing = ectopic or abnormal IUP
• Progesterone < 15 ng/mL: 81% sensitivity for ectopic
• Progesterone > 25 ng/mL: likely normal IUP
• Transvaginal ultrasound is the key imaging tool (no IUP seen + adnexal mass)
• "Discriminatory zone" hCG level: if hCG is above threshold and no IUP seen on TVU = ectopic until proven otherwise

• Hemodynamically unstable: immediate surgery
• Stable + unruptured: Methotrexate (single dose IM) - contraindicated in: renal/hepatic disease, immunodeficiency, thrombocytopenia, breastfeeding, cardiac/pulmonary disease
• Criteria for methotrexate: adnexal mass < 3.5 cm, no fetal cardiac activity, hCG < 5,000 mIU/mL (varies)
• Ruptured ectopic = surgical emergency

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4. POSTPARTUM HEMORRHAGE (PPH)

1. Bimanual uterine massage + fundal massage
2. Oxytocin 10-30 units in 1 L IV fluid (first-line uterotonic)
3. Methylergonovine 0.2 mg IM - CONTRAINDICATED in hypertension (causes vasoconstriction)
4. 15-methyl PGF2-alpha (Hemabate) 0.25 mg IM q 15-90 min - CONTRAINDICATED in asthma
5. Misoprostol (PGE1) - can be given rectally
6. Surgical: uterine compression sutures, uterine artery ligation, B-Lynch suture, hysterectomy (last resort)

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5. PLACENTA PREVIA vs PLACENTAL ABRUPTION

• NEVER do digital vaginal exam with placenta previa - can cause catastrophic hemorrhage
• Placenta previa "migrates" - 90% of 2nd trimester previas resolve by term
• Abruption: risk of DIC, Couvelaire uterus (blood into myometrium)
• Placenta accreta (invasion into myometrium) = major risk with prior C-section + placenta previa together

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6. PRETERM LABOR

• Nifedipine (calcium channel blocker) - preferred first-line
• Indomethacin (NSAID) - used < 32 weeks; avoid > 32 weeks (premature ductal closure)
• Magnesium sulfate (also used for fetal neuroprotection < 32 weeks)
• Beta-agonists (terbutaline) - less used due to side effects

• < 34 weeks: expectant management + antibiotics (ampicillin + azithromycin) + steroids
• Contraindication to tocolysis in PPROM

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7. CERVICAL CANCER SCREENING (USMLE Favorite)

• ASCUS: reflex HPV testing
• ASCUS + HPV negative: routine screening
• ASCUS + HPV positive: colposcopy
• LSIL (age 21-24): repeat Pap in 1 year
• LSIL (age 25+): colposcopy
• HSIL: colposcopy + biopsy (do NOT observe)
• Atypical Glandular Cells (AGC): always colposcopy (rule out endocervical/endometrial pathology)
• HPV 16 or 18 positive: direct colposcopy

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8. HIGH-YIELD GYNECOLOGY EXTRAS

• Premenopausal, functional cyst < 8 cm: watchful waiting, repeat U/S in 4-6 weeks
• Post-menopausal + adnexal mass: surgical evaluation (cancer until proven otherwise)
• CA-125 elevated in: ovarian epithelial cancer, but also endometriosis, fibroids, PID (not specific)
• Most common ovarian malignancy in adults: serous cystadenocarcinoma

• Classic triad: dysmenorrhea, dyspareunia, infertility
• "Chocolate cysts" (endometriomas) on ovary
• CA-125 may be elevated
• Diagnosis: laparoscopy (gold standard)
• Treatment: OCPs, GnRH agonists, progestins; surgery for severe or infertility cases

• Most common pelvic tumor in women
• Most common in African American women
• Symptoms: heavy menses, pelvic pressure, urinary frequency, infertility
• Shrink with menopause (estrogen-dependent)
• Malignant degeneration (leiomyosarcoma) rare but suspect if rapidly growing

• Rotterdam criteria (2 of 3): oligo/anovulation + hyperandrogenism + polycystic ovaries on U/S
• Labs: elevated LH:FSH ratio (> 2:1), elevated androgens, insulin resistance
• Treatment: OCPs (first-line for menstrual irregularity + hirsutism), metformin (insulin resistance), clomiphene/letrozole (if fertility desired)
• Associated: endometrial hyperplasia/cancer (from unopposed estrogen), metabolic syndrome

• Rule out: endometrial cancer first
• Workup: transvaginal ultrasound (endometrial stripe > 4-5 mm = biopsy)
• Most common cause: endometrial atrophy; most dangerous: endometrial cancer

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9. LABOR & DELIVERY PEARLS

• After delivery of head, anterior shoulder impacted behind pubic symphysis
• McRoberts maneuver (hyperflex legs) + suprapubic pressure (NOT fundal pressure) = first-line
• Never fundal pressure (worsens impaction)
• If fails: Rubin II, Woods screw, Zavanelli, posterior arm delivery

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10. QUICK HIT STEP 3 MNEMONICS

• 4 T's of PPH: Tone, Tissue, Trauma, Thrombin
• Methylergonovine contraindication: Hypertension
• Hemabate (PGF2a) contraindication: Asthma
• Magnesium antidote: Calcium gluconate
• First test in third trimester bleeding: Transvaginal U/S (placenta previa)
• First step in ectopic evaluation: Quantitative beta-hCG + transvaginal U/S
• GDM screening timing: 24-28 weeks
• HELLP treatment: Delivery
• Postmenopausal bleeding #1 workup: TVUS (endometrial stripe), then biopsy if > 4-5 mm

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USMLE Step 3 - Biostatistics & Ethics High-Yield Must-Knows

Step 3 Day 1 (Foundations of Independent Practice) is heavily weighted on biostatistics, epidemiology, and medical ethics - accounting for approximately 11-13% of the overall exam. These are free points if you know the formulas and frameworks cold.

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PART 1: BIOSTATISTICS

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THE 2x2 TABLE - Master This First

                    DISEASE +        DISEASE -
TEST POSITIVE          a (TP)           b (FP)
TEST NEGATIVE          c (FN)           d (TN)

• Higher prevalence → higher PPV, lower NPV
• Lower prevalence → lower PPV, higher NPV

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LIKELIHOOD RATIOS

• Positive LR = Sensitivity / (1 - Specificity)
• Negative LR = (1 - Sensitivity) / Specificity
• LR > 10 or < 0.1 generates large, often decisive changes in probability
• LR between 0.5 and 2.0 = small and usually not clinically important

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MEASURES OF ASSOCIATION

                    DISEASE +        DISEASE -
EXPOSED                a                b
NOT EXPOSED            c                d

• OR approximates RR when disease is rare (< 10% prevalence) - this is the rare disease assumption
• RR = 1.0 means no association; OR = 1.0 means no association
• NNT closer to 1 = more effective treatment; higher NNT = less effective
• Pharmaceutical ads on Step 3 love to present RRR (looks impressive) - always calculate ARR and NNT yourself

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STATISTICAL SIGNIFICANCE

• Wider CI = less precision = smaller sample size
• Narrower CI = more precision = larger sample size
• Increasing sample size increases power and narrows CIs
• Statistical significance ≠ clinical significance

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STUDY DESIGNS - Evidence Hierarchy

1. Systematic Review / Meta-analysis - pooled analysis of multiple RCTs
2. Randomized Controlled Trial (RCT) - gold standard for causation; experimental; randomization controls for confounding
3. Cohort Study - observational, follows exposed vs. unexposed forward in time; calculates RR; good for rare exposures
4. Case-Control Study - observational, compares cases vs. controls; looks backward at exposure; calculates OR; good for rare diseases
5. Cross-Sectional Study - prevalence study; snapshot in time; calculates prevalence ratio; no temporality
6. Case Series / Case Report - descriptive; no controls
7. Expert Opinion - lowest level

• Rare disease + want to study exposure → Case-control
• Rare exposure + want to study disease → Cohort
• Want to prove causation → RCT
• Prevalence of a condition → Cross-sectional
• Long-term risk in a population → Cohort

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BIAS - HIGH-YIELD TYPES

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SCREENING TEST PRINCIPLES

• High sensitivity (few false negatives - don't miss cases)
• Disease must have a detectable preclinical phase
• Effective treatment must exist
• Disease must be important (serious enough to warrant screening)
• Test must be acceptable, affordable, available

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READING A DRUG AD (Classic Step 3 Format)

1. Find the ARR (not just RRR - companies always advertise RRR)
2. Calculate NNT = 1/ARR
3. Check the 95% CI - does it include 1.0 (for ratios) or 0 (for differences)?
4. Check P-value < 0.05?
5. Ask: is this statistically significant AND clinically meaningful?
6. What study design was used? Can you establish causation?

• ARR = 4% - 2% = 2% = 0.02
• NNT = 1/0.02 = 50 (need to treat 50 patients to prevent 1 MI)
• RRR = 2%/4% = 50% (the number the drug company advertises)

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PART 2: MEDICAL ETHICS

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THE FOUR CORE PRINCIPLES

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DECISION-MAKING CAPACITY

1. Understand - comprehend their condition and the proposed treatment
2. Appreciate - apply the information to their own situation
3. Reason - rationally weigh options and consequences
4. Express - communicate a consistent choice

• Capacity = clinical determination (assessed by physician at bedside)
• Competence = legal determination (made by a judge)
• A patient can have capacity for some decisions but not others
• Psychiatric patients CAN have decision-making capacity if the above criteria are met
• A patient who is suicidal does NOT automatically lack capacity for all decisions - assess case by case

1. Check for advance directive (living will, POLST/MOLST)
2. If none, use healthcare proxy/durable power of attorney for healthcare (designated person)
3. If none, next of kin (spouse → adult children → parents → siblings)
4. Court-appointed guardian if no surrogate available

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INFORMED CONSENT

1. Voluntariness - free of coercion; patient decides freely
2. Information - physician discloses diagnosis, proposed treatment, alternatives, risks/benefits, consequences of refusal
3. Capacity - patient has decision-making capacity

• Emergency - patient incapacitated and immediate intervention needed to prevent serious harm/death
• Waiver - patient explicitly waives the right to information
• Therapeutic privilege - rarely applicable; physician withholds information only if disclosure itself would harm the patient (very narrow exception, not used to avoid difficult conversations)
• Public health/legal mandate - e.g., court-ordered treatment

• Generally, parents consent for children
• Exceptions (mature minor / emancipated minor can consent for themselves): STIs, contraception, pregnancy, substance abuse treatment, mental health (varies by state)
• Emancipated minor = married, military, financially independent, or living independently

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CONFIDENTIALITY

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END-OF-LIFE ETHICS

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SURROGATE DECISION-MAKING STANDARD

1. Substituted judgment - what would the patient have wanted? (best standard)
2. Best interest - what is objectively in the patient's best interest? (used when patient's wishes unknown)

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HIGH-YIELD ETHICS SCENARIOS FOR STEP 3

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RESEARCH ETHICS (Belmont Report Principles)

• Respect for persons - voluntary participation + informed consent; extra protection for vulnerable populations (prisoners, children, pregnant women, cognitively impaired)
• Beneficence - maximize benefits, minimize harms
• Justice - equitable selection of research subjects; don't exploit vulnerable populations

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QUICK-HIT FORMULAS CHEAT SHEET

Sensitivity    = TP / (TP + FN)           = a / (a+c)
Specificity    = TN / (TN + FP)           = d / (b+d)
PPV            = TP / (TP + FP)           = a / (a+b)
NPV            = TN / (TN + FN)           = d / (c+d)

RR             = [a/(a+b)] / [c/(c+d)]
OR             = (a×d) / (b×c)
ARR            = Risk(control) - Risk(treatment)
NNT            = 1 / ARR
RRR            = 1 - RR  (or ARR / control risk)

Power          = 1 - β
Type I (α)     = 0.05 → false positive (study says effective, but it's not)
Type II (β)    = 0.20 → false negative (study says no effect, but there is one)

95% CI for ratio: does NOT include 1.0 → statistically significant
95% CI for difference: does NOT include 0 → statistically significant

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USMLE Step 3 - Internal Medicine High-Yield Must-Knows (Full Overview)

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1. CARDIOLOGY

Acute Coronary Syndrome (ACS)

• Primary PCI within 90 minutes (door-to-balloon) if cath lab available = preferred
• Fibrinolysis (tPA, streptokinase) within 30 minutes if PCI not available within 120 min
• Fibrinolysis CONTRAINDICATIONS: prior intracranial hemorrhage, stroke within 3 months, active bleeding, aortic dissection, head trauma, BP > 180/110

• Aspirin immediately (all ACS) + P2Y12 inhibitor (clopidogrel, ticagrelor, prasugrel)
• Anticoagulation: heparin (UFH or LMWH)
• Beta-blockers within 24 hrs (avoid if acute decompensated HF, cardiogenic shock, bradycardia)
• Statin (high-intensity: atorvastatin 80 mg) within 24 hrs
• ACE inhibitor/ARB within 24 hrs (especially if EF reduced, anterior MI, DM, HTN)
• Aldosterone antagonist (eplerenone/spironolactone) if EF < 40% + HF or DM

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Heart Failure (HF)

• ACE inhibitor or ARB (if ACE-intolerant due to cough → ARB; if both tolerated → ARNI sacubitril/valsartan preferred over ACEi)
• Beta-blocker (carvedilol, metoprolol succinate, bisoprolol - only these 3 are proven)
• Aldosterone antagonist (spironolactone/eplerenone) - if EF < 35%, class II-IV symptoms
• SGLT2 inhibitor (dapagliflozin, empagliflozin) - now standard of care; reduces hospitalization and CV death
• Diuretics (furosemide) - symptom relief ONLY, no mortality benefit
• Hydralazine + nitrate - alternative if ACEi/ARB not tolerated (especially in Black patients)

• Diuresis (IV furosemide)
• Position: sit upright
• Supplemental O2; BiPAP for respiratory distress
• Vasodilators (nitrates, nitroprusside) for afterload reduction if BP adequate
• Avoid beta-blockers in acute decompensation

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Atrial Fibrillation (AF)

• Rate control (beta-blocker, CCB, digoxin) = preferred for most chronic AF
• Rhythm control (cardioversion, antiarrhythmics) = preferred for new-onset < 48 hrs, younger patients, symptomatic despite rate control

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Hypertensive Emergency

• BP > 180/120 + end-organ damage (encephalopathy, papilledema, AKI, MI, aortic dissection)
• Lower BP by no more than 25% in the first hour, then to 160/100 over next 2-6 hrs
• Drug: IV labetalol, nicardipine, or clevidipine
• Aortic dissection: target SBP 100-120, use labetalol + nitroprusside
• Hypertensive urgency = BP > 180/120 without end-organ damage → oral agents, no emergency

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2. PULMONOLOGY

COPD Exacerbation

• Short-acting bronchodilators (albuterol + ipratropium)
• Systemic corticosteroids (prednisone 40 mg x 5 days)
• Antibiotics if: increased sputum purulence + increased dyspnea (azithromycin, doxycycline, or Augmentin)
• Supplemental O2: target SpO2 88-92% (avoid O2 toxicity in CO2 retainers)
• BiPAP/NIV for hypercapnic respiratory failure (pH < 7.35, PaCO2 elevated) = reduces intubation rate

• All: SABA (albuterol) PRN
• Moderate+: LAMA (tiotropium) ± LABA
• Severe/frequent exacerbations: LAMA + LABA + ICS triple therapy
• Prophylactic azithromycin for frequent exacerbators

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Pulmonary Embolism (PE)

• 4 = high probability → go straight to CT-PA

• ≤ 4 = low/intermediate → D-dimer first; if elevated → CT-PA

• Provoked (identifiable reversible cause): 3 months
• Unprovoked/idiopathic: at least 3 months, consider indefinite
• Malignancy-associated: LMWH or DOAC preferred; indefinite while cancer active

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Pneumonia (CAP)

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3. NEPHROLOGY / RENAL

Acute Kidney Injury (AKI) - 3 Types

• Tubules: ATN (most common intrinsic cause)
• Glomeruli: glomerulonephritis (RBC casts in urine)
• Interstitium: AIN (WBC casts, eosinophiluria - often drug-induced)
• Vascular: TTP/HUS, malignant HTN

• Acidosis (pH < 7.1)
• Electrolytes (hyperkalemia refractory to treatment)
• Ingestion (toxic - methanol, ethylene glycol, aspirin)
• Overload (volume overload refractory to diuretics)
• Uremia (symptomatic - encephalopathy, pericarditis, bleeding)

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Electrolytes - High-Yield

1. Assess osmolality (pseudohyponatremia if normal/high)
2. Assess volume status (hypo-, eu-, hypervolemic)
3. Key causes: SIADH (euvolemic, low urine Na < 20 if restricted but urine Na > 20 with normal intake), cirrhosis/CHF (hypervolemic), true depletion (hypovolemic)

1. Calcium gluconate (stabilizes cardiac membrane - first and fastest)
2. Insulin + dextrose (shifts K into cells)
3. Sodium bicarbonate (metabolic acidosis)
4. Albuterol nebulization (shifts K)
5. Kayexalate/patiromer (eliminates K)
6. Dialysis (definitive if refractory)

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4. ENDOCRINOLOGY

Diabetes Mellitus

• Fasting glucose ≥ 126 mg/dL (x2)
• 2-hr OGTT glucose ≥ 200 mg/dL
• Random glucose ≥ 200 + symptoms
• HbA1c ≥ 6.5%

1. Metformin (first-line unless contraindicated - GFR < 30)
2. Add: SGLT2 inhibitor (if CV disease or CKD → proven mortality benefit); GLP-1 agonist (if CV disease, weight loss needed)
3. Sulfonylurea (cheap but risk of hypoglycemia); DPP-4 inhibitor (weight neutral)
4. Insulin (basal → basal-bolus) when HbA1c not at goal

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Thyroid

• Graves' disease (most common): diffuse goiter + ophthalmopathy + pretibial myxedema + TSH receptor antibodies (TRAb)
• Treatment: methimazole (preferred; PTU in 1st trimester), RAI, or surgery

• Treat: PTU → then iodine (at least 1 hr after PTU) → beta-blocker + corticosteroids + cooling

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5. GASTROENTEROLOGY / HEPATOLOGY

Upper GI Bleed

• 2 large-bore IVs; type & cross; NPO
• Resuscitate with IV fluids and pRBCs (target Hgb ≥ 7 g/dL; ≥ 8 if CAD)
• Proton pump inhibitor IV bolus (pantoprazole 80 mg) → drip
• EGD within 24 hours (within 12 hrs if hemodynamically unstable/stigmata of variceal bleed)
• Varices: octreotide drip + antibiotics (prophylactic ceftriaxone in cirrhosis) + banding at EGD

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Cirrhosis Complications

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6. HEMATOLOGY

Anemia Workup

• Microcytic (MCV < 80): Iron deficiency (most common), thalassemia, anemia of chronic disease (usually normocytic), sideroblastic anemia
• Normocytic (MCV 80-100): Anemia of chronic disease, aplastic anemia, renal failure (EPO deficiency), hemolysis, acute blood loss
• Macrocytic (MCV > 100): B12/folate deficiency (megaloblastic), alcohol, hypothyroidism, medications (hydroxyurea, methotrexate)

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DVT/PE Anticoagulation Quick Reference

• First-line (non-cancer): Apixaban or rivaroxaban (DOACs - start directly, no bridging)
• Cancer-associated: LMWH (enoxaparin) or DOAC (rivaroxaban, edoxaban)
• Pregnancy: LMWH only (warfarin and DOACs contraindicated)
• HIT (Heparin-Induced Thrombocytopenia): Stop ALL heparin; use argatroban, bivalirudin, or fondaparinux

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7. INFECTIOUS DISEASE

Sepsis (Surviving Sepsis Campaign)

1. Measure lactate; remeasure if initial > 2 mmol/L
2. Blood cultures x2 before antibiotics
3. Broad-spectrum antibiotics within 1 hour
4. 30 mL/kg crystalloid (IV fluids) for hypotension or lactate ≥ 4
5. Vasopressors (norepinephrine = first-line) if MAP < 65 despite fluids
6. Reassess with repeat lactate if > 2 mmol/L

• Vasopressin if norepinephrine > 0.25-0.5 mcg/kg/min
• Dobutamine if cardiogenic component (low CO)
• Hydrocortisone 200 mg/day if vasopressor-refractory shock

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HIV/AIDS

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8. NEUROLOGY

Ischemic Stroke

• Within 3-4.5 hours of symptom onset (or last known well time)
• BP must be < 185/110 before tPA
• No hemorrhage on non-contrast CT

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Seizures

1. Benzodiazepine (lorazepam 0.1 mg/kg IV, or diazepam, or midazolam IM) = first-line
2. Second-line: levetiracetam, fosphenytoin, or valproate IV
3. Third-line: propofol, midazolam drip, or barbiturate coma

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9. RHEUMATOLOGY

High-Yield Autoimmune Diseases

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10. QUICK-HIT STEP 3 PEARLS

• ACS + Heparin → always check platelets on day 5-7 (HIT risk)
• Metformin hold before IV contrast if GFR borderline; restart 48 hrs after if creatinine stable
• ACEi + K-sparing diuretic + NSAIDs = triple whammy → AKI
• NSAID use → raises BP, worsens CHF, causes AKI, blocks aspirin (take aspirin 2 hrs before)
• Warfarin reversal: Vitamin K (gradual), FFP (immediate), 4-factor PCC (fastest)
• Dabigatran reversal: Idarucizumab (specific antidote)
• Rivaroxaban/Apixaban reversal: Andexanet alfa
• Lidocaine toxicity signs: Circumoral numbness → seizures → cardiac arrest (C > CNS > cardiac)
• Rhabdomyolysis: Elevated CK, myoglobinuria (tea-colored urine), AKI → aggressive IV fluids
• Transfusion thresholds: Hgb < 7 (most pts); < 8 (ACS, symptomatic); < 10 (bone marrow failure)

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