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📚 Module 4 — OB Exam Master Guide

Based on Williams Obstetrics

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TABLE OF CONTENTS

1. Obstetrical Analgesia & Anesthesia
2. Vaginal Delivery
3. Breech Presentation & Delivery
4. Operative Vaginal Delivery
5. Cesarean Delivery
6. Peripartum Complications
7. Prior Cesarean / VBAC

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1. OBSTETRICAL ANALGESIA & ANESTHESIA {#1}

Overview

• Skill and experience of the provider
• Stage and progress of labor
• Maternal/fetal complications
• Patient preference

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A. Parenteral (Systemic) Analgesia

⚠️ Key point: Systemic opioids do not truly relieve labor pain — they reduce anxiety and cause sedation. All cross the placenta and cause dose-dependent neonatal sedation.

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B. Regional (Epidural) Analgesia

• Bupivacaine — more prolonged, slower onset
• Chloroprocaine — faster onset
• Combinations of local anesthetics + narcotics — excellent analgesia with less motor blockade (allows ambulation)

Exam pearl: The Zhang study showed that when epidural rate suddenly jumped from 1% → 84%, there was no change in C-section rate, operative delivery rate, or first-stage duration. Only the second stage was prolonged by 25 min. This is definitive evidence that epidural ≠ increased C-section risk.

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C. Anesthesia Types Summary

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2. VAGINAL DELIVERY {#2}

The Three P's of Labor

1. Powers — uterine muscular forces
2. Passenger — size and orientation of fetus
3. Passage — bony pelvis + soft tissue of pelvic floor

Seven Cardinal Movements of Labor

1. Engagement
2. Descent
3. Flexion
4. Internal rotation
5. Extension
6. External rotation (restitution)
7. Expulsion

Prerequisites for Safe Vaginal Delivery

• No absolute CPD (cephalopelvic disproportion)
• Adequate progress of labor
• No contraindications (e.g., placenta previa, vasa previa, certain malpresentations, active herpes)

Episiotomy

• Mediolateral preferred in many countries; median (midline) common in US
• Routine episiotomy is NOT recommended — restrict to specific indications (imminent severe laceration, operative delivery, fetal distress)

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3. BREECH PRESENTATION & DELIVERY {#3}

Incidence & Etiology

• Occurs in 3–4% of all deliveries at term
• Decreases with advancing gestation:
  • 24% at 18–22 wks → 7% at 34 wks → 2.8% at 38–40 wks
• Associated with fundal-cornual placental implantation (occurs in only 7% of pregnancies)
• Also associated with neuromuscular disorders, congenital anomalies, diminished fetal muscle tone

Types of Breech

Risks of Breech Delivery

1. Prolapse of umbilical cord — especially footling breech
2. Trapping of the after-coming head — especially in preterm < 1500 g or with CPD; cervix fully dilated for body but not for head
3. Head/arm trauma — from extension of head or nuchal arm position

External Cephalic Version (ECV)

• Offered at 36–37 weeks
• Reduces need for cesarean
• Success rate ~50–60%
• Contraindications: placenta previa, prior uterine scar (relative), oligohydramnios, multiple gestation

Term Breech Delivery — Current Practice

• The Term Breech Trial (Hannah, 2000) established that planned cesarean delivery is safer than planned vaginal delivery for term breech → dramatically increased C-section rates for breech
• Vaginal breech delivery is still performed in selected cases with experienced providers
• Prelabor cesarean is the dominant management for term breech in most centers

Breech Vaginal Delivery Technique (if attempted)

• Frank breech most favorable for vaginal delivery
• Allow spontaneous delivery to umbilicus
• Pinard maneuver — for delivery of legs in frank breech
• Mauriceau-Smellie-Veit maneuver — for delivery of after-coming head
• Piper forceps — applied to after-coming head to control delivery
• Avoid pulling on the body before the head is at the inlet (risk of hyperextension)

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4. OPERATIVE VAGINAL DELIVERY {#4}

Overview

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A. Obstetric Forceps

ACOG Classification (1988) — High-Yield!

Exam pearl: When reclassified by modern ACOG criteria, mid-forceps are associated with significantly lower cord pH values and higher incidence of fetal injury compared with outlet/low forceps. The critical dividing line is +2 cm station.

Indications for Forceps

• Arrest of labor in second stage
• Maternal indication for shortening second stage (cardiac/cerebrovascular disease, maternal exhaustion)
• Fetal distress
• Elective low-pelvic delivery

Prerequisites (ALL must be met):

• Cervix fully dilated
• Membranes ruptured
• Head engaged
• Position of head known
• Pelvis adequate
• No CPD
• Bladder emptied
• Adequate anesthesia

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B. Vacuum Extraction

• Arrest in second stage
• Shorten second stage (maternal cardiac/cerebrovascular indication)
• Fetal distress
• Elective low-pelvic delivery

• CPD
• Face or brow presentation
• Breech presentation
• Unengaged fetal head
• Premature infant
• Incompletely dilated cervix

Vacuum vs. Forceps — Comparison (Johanson & Menon Systematic Review)

⚠️ CRITICAL EXAM POINT — Sequential Use: Combining vacuum then forceps (or vice versa) is dangerous. Risk of intracranial hemorrhage with both instruments = 7.4× greater than spontaneous delivery and 3.4× greater than vacuum alone. ACOG recommends avoiding sequential use.

• Easier to apply and learn
• Less anesthesia required
• No increase in traction force beyond what head can tolerate (cup pops off)

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5. CESAREAN DELIVERY {#5}

Historical Milestones

• Pre-20th century: mortality ≥ 85%
• Key innovations: aseptic technique, reliable anesthesia, hemorrhage control, low-segment incision (reduced peritonitis risk)
• D'Esopo (1950): first report of 1000 consecutive C-sections without maternal death
• Blood transfusion + antibiotics further reduced morbidity

Incidence Trends

• Pre-1960: < 5% of births (primarily maternal indications)
• US peak: 23.5% in 1988
• Four indications accounted for 90% of increase: dystocia, repeat cesarean, breech, fetal distress
• Dystocia alone = 30% of the increase

Types of Uterine Incision

Indications for Cesarean (Williams framework)

C-section is indicated any time delivery must occur and vaginal delivery carries greater risk to mother or fetus than abdominal delivery.

1. Dystocia / CPD — #1 cause of primary cesarean
2. Repeat cesarean (prior classic or multiple scars)
3. Breech presentation (especially after Term Breech Trial)
4. Fetal distress (non-reassuring FHR)
5. Placenta previa / accreta spectrum
6. Cord prolapse
7. Active genital herpes at onset of labor
8. Fetal anomalies (gastroschisis, large myelomeningocele)
9. Failed operative vaginal delivery (higher risk if cesarean after failed vacuum/forceps)

Maternal Complications of Cesarean

• Anesthesia accidents (intubation failure, aspiration pneumonitis, drug reactions)
• Hemorrhage
• Bladder/bowel injury — urinary tract injury 10× more common in C-section vs. operative vaginal delivery (1–2 per 1000 deliveries)
• Amniotic fluid embolism
• Air embolism

• Atelectasis
• Endomyometritis
• Urinary tract infection
• Wound complications (hematoma, dehiscence, infection, necrotizing fasciitis)
• Thromboembolic disease
• Bowel dysfunction — ileus, Ogilvie syndrome (pseudoobstruction of cecum), sigmoid volvulus

• Lilford et al: 7× relative risk of death vs. vaginal delivery (when pre-existing conditions excluded)
• Nonelective vs. elective cesarean: 1.5× greater risk
• With prophylactic antibiotics: dramatically reduced febrile complications

Perioperative Antibiotic Prophylaxis

• Standard: Cefazolin 2 g IV (for patients < 120 kg) before incision
• For patients ≥ 120 kg: Cefazolin 3 g IV
• Joint guideline (ASHP/IDSA/SIS/SHEA 2013): above dosing recommendations

Fetal/Neonatal Complications

• Risk of intracranial hemorrhage: no significant difference between vacuum, forceps, and cesarean (for patients where spontaneous delivery failed) — Towner study of 583,340 liveborn singletons
• However: Cesarean after failed operative vaginal delivery = significantly greater neonatal morbidity than cesarean without prior attempt

Pelvic Floor Considerations

• Urinary incontinence at 6 months: 2× greater after spontaneous vaginal delivery vs. cesarean
• Relative risk of incontinence at 3 months: 0.62 (62% less risk with cesarean)
• This has driven debate about elective cesarean for nulliparas — insufficient evidence to recommend routine elective cesarean for pelvic floor protection

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6. PERIPARTUM COMPLICATIONS {#6}

Peripartum Cardiomyopathy (PPCM)

• New-onset heart failure in the last month of pregnancy or within 5 months postpartum, with no other cause identified
• LV systolic dysfunction (EF < 45%)
• Risk factors: older age, multiparity, pre-eclampsia, African American ethnicity, twins
• Management: standard heart failure therapy; bromocriptine (controversial, investigational); delivery if unstable
• Recovery: ~50% recover LV function; ~10–15% require transplant or die

Obstetric Hemorrhage

• PPH definition: > 500 mL vaginal delivery; > 1000 mL cesarean
• "4 T's" of PPH:
  • Tone (uterine atony — 70–80% of PPH)
  • Trauma (lacerations, uterine rupture, hematoma)
  • Tissue (retained placenta, accreta spectrum)
  • Thrombin (coagulopathy)

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7. PRIOR CESAREAN / VBAC {#7}

Key Principle

VBAC (Vaginal Birth After Cesarean) / TOLAC (Trial of Labor After Cesarean)

Induction/Ripening with Prior Scar

Risk of Uterine Rupture

• Prior low transverse: ~0.5–0.9% with TOLAC
• Prior classic: 1–12% — hence mandatory repeat cesarean
• Signs: fetal bradycardia, loss of station, maternal abdominal pain, maternal hemorrhage

VBAC Success Predictors

• Prior vaginal delivery (strongest predictor of VBAC success)
• Spontaneous onset of labor
• No recurrent indication (e.g., non-recurrent fetal distress vs. recurrent CPD)

Stillbirth and Prior Cesarean (Special Scenario)

• For women with prior C-section and fetal demise: repeat cesarean should ideally be avoided
• Low transverse < 28 wks: misoprostol acceptable
• Low transverse > 28 wks: oxytocin ± Foley balloon
• Studies show TOLAC results in vaginal delivery in 91.1% of women with prior C-section and fetal demise, with rare uterine rupture

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HIGH-YIELD EXAM SUMMARY TABLE

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QUICK MNEMONICS

• Prolapse of cord (especially footling)
• Trapping of after-coming head
• Arm/head trauma (nuchal arm, extension)

• Tone (atony) — 70–80%
• Trauma
• Tissue
• Thrombin

• Cervix fully dilated
• Engaged head
• Ruptured membranes
• Vertex position confirmed
• No Inadequate pelvis/CPD
• X-tra: bladder empty, anesthesia adequate

• Scalp visible at introitus → Outlet
• Station +2 or lower → Low
• Station above +2 (but engaged) → Mid

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EXAM APPROACH TIPS

1. Epidural questions: The answer is almost always "epidural does NOT increase C-section rate" — the only effect is prolonging second stage by ~25 min.
2. Breech at term: The standard of care is cesarean, but ECV at 36–37 wks should be offered first.
3. Forceps vs. vacuum: Vacuum has less maternal trauma but more fetal scalp complications. Never use both sequentially.
4. Prior classic incision: Always requires repeat cesarean. Low transverse is eligible for TOLAC.
5. Meperidine reversal: Naloxone 0.1 mg/kg IV/IM for neonatal depression.
6. C-section antibiotics: 2 g cefazolin < 120 kg; 3 g cefazolin ≥ 120 kg, given BEFORE incision.
7. Dystocia is the single biggest driver of cesarean delivery rates (30% of the increase in the US).

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What's Covered:

1. Analgesia & Anesthesia — Systemic opioids (meperidine dosing, naloxone reversal), epidural drugs (bupivacaine vs. chloroprocaine), and the critical exam fact that epidural does NOT increase C-section rate — it only prolongs the second stage by 25 minutes.
2. Vaginal Delivery — The 3 P's (Powers, Passenger, Passage), 7 cardinal movements, and episiotomy.
3. Breech Presentation — Incidence by GA, 3 types, 3 risks (cord prolapse, head trapping, trauma), ECV, and when to do cesarean vs. vaginal.
4. Operative Vaginal Delivery — Full ACOG forceps classification (outlet/low/mid), prerequisites for application, vacuum (Malmström 1954), vacuum vs. forceps comparison, and the critical sequential-use warning (7.4× ICH risk).
5. Cesarean Delivery — History, incidence trends, incision types, indications, maternal complications, antibiotic prophylaxis dosing (2 g vs. 3 g cefazolin by weight), and pelvic floor data.
6. Prior Cesarean/VBAC — Low transverse = TOLAC eligible; classic = mandatory repeat C-section (1–12% rupture risk); induction protocols by gestational age and scar type.