High-Yield OB/GYN for USMLE Step 3: Preeclampsia, Labor, and Postpartum Hemorrhage

Nobody feels ready for an OB emergency. Not as a third-year student, not as an intern, and honestly — not the first time you're running one as an attending either. But Step 3 doesn't care about your comfort level. It's going to hand you a seizing 32-weeker or a postpartum hemorrhage and expect you to act in seconds, not minutes. OB/GYN questions are where the exam shifts from "what do you know" to "what do you do first, second, third."

I've watched residents ace cardiology and renal, then freeze on a CCS obstetric case because the stakes feel different when there are two patients. Here's how to not be that person.

Hypertensive Disorders of Pregnancy

Preeclampsia

This gets tested relentlessly, and for good reason — it's the condition where missing one diagnostic criterion changes your entire management plan.

Diagnosis criteria (after 20 weeks gestation):

• BP ≥ 140/90 mmHg on two occasions ≥ 4 hours apart
• PLUS at least one of: proteinuria (> 300 mg/24h, protein/creatinine ratio ≥ 0.3, or dipstick ≥ 2+)
• OR severe features (can diagnose WITHOUT proteinuria if severe features present)

That last bullet is where the exam sets its trap. I've seen countless practice answers where students rule out preeclampsia because the urine protein is negative. Wrong. You don't need proteinuria if severe features are present. The ACOG criteria changed years ago, but the old "preeclampsia = hypertension + proteinuria" definition still lives in people's heads.

Severe features of preeclampsia:

• BP ≥ 160/110 mmHg
• Thrombocytopenia (platelets < 100,000)
• Renal insufficiency (Cr > 1.1 or doubling without other cause)
• Impaired liver function / right upper quadrant pain / epigastric pain
• Pulmonary edema
• New-onset headache unresponsive to medication OR visual disturbances

HELLP Syndrome: Hemolysis + Elevated Liver enzymes + Low Platelets — a severe variant. Deliver regardless of gestational age. Full stop. Don't let the 28-week gestational age tempt you into expectant management.

Management

Definitive treatment = delivery. Everything else is just buying time.

• ≥ 37 weeks: deliver for any preeclampsia
• 34–37 weeks: deliver for severe features or maternal/fetal deterioration
• < 34 weeks: consider expectant management in select patients without severe features (betamethasone for fetal lung maturation)

Magnesium sulfate: seizure prophylaxis for preeclampsia with severe features — loading dose 4–6g IV, then 1–2g/hr maintenance. Monitor for toxicity (loss of DTRs at Mg 7–10, respiratory depression > 10, cardiac arrest > 15); antidote: calcium gluconate.

Blood pressure control: labetalol IV (first-line), hydralazine IV, nifedipine oral — target BP < 160/110.

Here's the distinction that generates wrong answers on every practice exam I've reviewed: magnesium sulfate does NOT lower blood pressure. It prevents seizures. That's it. You need separate antihypertensives running simultaneously. When a CCS case gives you a preeclamptic patient at 160/112 with headache, the correct sequence is magnesium AND labetalol — not one or the other.

Labor and Delivery

Normal Labor Stages

Seems basic, but Step 3 tests your understanding of what's abnormal — and you can't spot abnormal without knowing normal cold.

Stage 1: onset of regular contractions → complete cervical dilation (10 cm)

• Latent phase: 0–6 cm (slow progress is normal — this is where people jump to C-section too early)
• Active phase: 6–10 cm (normal progress ≥ 1 cm/hour)

Stage 2: complete dilation → delivery of infant

Stage 3: delivery of infant → delivery of placenta (up to 30 minutes is normal)

A contrarian point most review courses won't make: the biggest mistake on Step 3 labor questions isn't missing an emergency — it's intervening too early in latent labor. The exam tests patience as much as action. A primipara at 4 cm who's been contracting for 10 hours? That can be normal. Calling that "failure to progress" and rushing to augmentation or cesarean delivery is a classic wrong answer.

Shoulder Dystocia

When the fetal shoulder impales behind the maternal pubic symphysis after head delivery. You'll recognize it by the "turtle sign" — the fetal head delivers, then retracts back against the perineum. The clock starts now.

Management sequence (HELPERR):

• H — Call for Help
• E — Evaluate for Episiotomy
• L — Legs (McRoberts maneuver — hyperflexion of maternal thighs against abdomen)
• P — Suprapubic Pressure
• E — Enter (rotational maneuvers: Rubin II, Woods screw)
• R — Remove posterior arm
• R — Roll to all-fours (Gaskin maneuver)

The single most tested detail in this entire mnemonic: it's suprapubic pressure, not fundal pressure. Fundal pressure worsens the impaction and can cause uterine rupture. Every year this shows up, and every year it catches people. If you remember nothing else from this section, remember that.

McRoberts + suprapubic pressure resolves the vast majority of shoulder dystocias. The subsequent steps exist for the cases that don't resolve — but the exam usually wants you to start there.

Postpartum Hemorrhage

Definition: blood loss > 500 mL after vaginal delivery or > 1,000 mL after cesarean section.

When I was on OB as a resident, a senior attending told me: "The first thing you do for a postpartum hemorrhage is massage the uterus. The second thing you do is ask yourself why the uterus is boggy." That framing stuck. And it maps perfectly to the 4Ts.

4 Ts of PPH

Cause	Frequency	Examples
Tone (uterine atony)	80%	Overdistended uterus (polyhydramnios, macrosomia, multiples), prolonged labor, grand multiparity
Trauma	15%	Cervical/vaginal lacerations, uterine rupture
Tissue	5%	Retained placenta, placenta accreta spectrum
Thrombin	< 1%	Pre-existing coagulopathy, DIC, abruption

Uterine atony dominates — 80% of cases. The exam knows you know this. So it'll give you atony as the obvious answer, then describe a firm uterus with continued bleeding. That's when you pivot to Trauma or Tissue. The firm-uterus trick is worth knowing cold.

Management of uterine atony (Tone):

1. Bimanual uterine massage
2. Oxytocin IV (first-line uterotonic)
3. Methylergonovine (ergot alkaloid) — contraindicated in hypertension
4. Carboprost (prostaglandin F2α) — contraindicated in asthma (bronchospasm)
5. Misoprostol (can use rectally or sublingually)
6. Tranexamic acid IV — reduces mortality if given within 3 hours

Those contraindications are tested more than the drugs themselves. Preeclamptic patient bleeding? No methylergonovine — you'll spike her blood pressure. Asthmatic patient with atony? No carboprost — you'll bronchospasm her. The exam builds the clinical scenario around these contraindications deliberately.

Surgical options if medical management fails: uterine balloon tamponade → uterine compression sutures (B-Lynch) → uterine artery ligation → hysterectomy (definitive, last resort).

Ectopic Pregnancy

Classic triad: lower abdominal pain + amenorrhea + vaginal bleeding. But here's reality — the full triad is present in fewer than half of cases. The exam may give you just one or two of these with a positive pregnancy test. Maintain suspicion.

Beta-hCG elevated but not rising normally (< 66% increase in 48 hours is abnormal for an intrauterine pregnancy).

Diagnosis: transvaginal ultrasound + serial beta-hCG. The "discriminatory zone" is the critical concept — if hCG > 1,500–2,000 mIU/mL and no intrauterine pregnancy seen on TVUS, it's ectopic until proven otherwise. Don't wait for a "definitive" ultrasound finding. This is a clinical decision point, not a radiologic one.

Management:

• Methotrexate (single IM dose): unruptured, hemodynamically stable, sac < 3.5 cm, no fetal cardiac activity, hCG < 5,000, no contraindications (renal/liver disease, blood dyscrasia)
• Surgery (laparoscopic salpingectomy): ruptured ectopic, hemodynamically unstable, or methotrexate failure/contraindicated

The CCS case for ectopic usually tests one specific skill: recognizing the unstable patient who needs surgery now versus the stable patient eligible for methotrexate. If there's free fluid in the cul-de-sac with tachycardia, don't order a methotrexate level — get her to the OR.

Gynecological Cancer Screening

Cervical Cancer Screening (Pap Smear)

This is pure memorization, but the intervals trip people up constantly:

• Begin at age 21 (regardless of sexual activity onset)
• 21–29: Pap smear alone every 3 years
• 30–65: Co-testing (Pap + HPV) every 5 years OR Pap alone every 3 years
• Stop at 65 with adequate prior negative screening

HPV vaccination: 9-valent (Gardasil 9) — recommended at 11–12 years; catch-up through age 26 for all; shared decision-making 27–45 years.

The detail that surprises most test-takers: screening starts at 21 regardless of when sexual activity began. A 19-year-old who's been sexually active for 3 years? No Pap yet. A 21-year-old who's never been sexually active? Screen her. The age cutoff is firm, and the exam loves presenting the 19-year-old as a distractor.

FAQ

How heavily is OB/GYN tested on Step 3?

Expect 8–12% of your exam to involve OB/GYN content. More importantly, CCS virtually guarantees at least one obstetric case — usually a labor management or obstetric emergency scenario. These cases feel high-stakes because the simulated clock runs and order timing matters for scoring.

What's the most commonly tested OB/GYN topic on Step 3?

Preeclampsia, and it's not close. The condition spans diagnosis, management, medication dosing, and delivery timing — the exam can ask it five different ways. Postpartum hemorrhage is second. If you're short on time, those two topics alone cover the majority of OB/GYN questions.

Do I need to know the Bishop score for Step 3?

Know the concept (cervical favorability assessment before labor induction), but don't memorize the point breakdown. The exam is more likely to describe a clinical scenario — "cervix is 1 cm dilated, firm, posterior, and long" — and ask whether you'd induce or ripen. Knowing that an unfavorable cervix needs prostaglandin ripening before oxytocin is the testable point.

How should I approach a CCS case with a pregnant patient?

Think in trimester-specific frameworks. First trimester: ectopic, miscarriage, hyperemesis. Second trimester: anatomy scan findings, cervical insufficiency. Third trimester: preeclampsia, labor, hemorrhage. Then remember the delivery decision — the CCS exam frequently tests whether you choose expectant management or delivery at a given gestational age. Getting that decision right is often worth more than the subsequent orders.

What OB/GYN drug contraindications are most tested?

Three pairings show up repeatedly: methylergonovine is contraindicated in hypertension, carboprost is contraindicated in asthma, and methotrexate is contraindicated in ectopic pregnancy with fetal cardiac activity (or hemodynamic instability). The exam builds clinical vignettes around these contraindications — they're designed so the "obvious" drug choice is actually the wrong one for that specific patient.

Put It Into Practice

OB/GYN on Step 3 rewards decisive action under time pressure. The algorithms are learnable — what separates high scorers is practicing them until the sequence is automatic, not something you're reconstructing from memory mid-case.

Step3Sim offers free USMLE Step 3 practice questions for obstetrics-gynecology and all other organ systems — including CCS simulations where delivery timing and order sequencing are scored exactly like the real exam.