What is the most common cause of postpartum hemorrhage (PPH) after a spontaneous vaginal delivery (SVD)?

Most Common Cause of Postpartum Hemorrhage After SVD

The correct answer is B - Atony. Uterine atony is the most common cause of postpartum hemorrhage, accounting for more than 75% of cases after vaginal delivery. 1

Evidence-Based Hierarchy of PPH Causes

Uterine Atony (Most Common)

• Uterine atony accounts for 70-80% of all postpartum hemorrhage cases and is the leading cause of early PPH (within first 24 hours after delivery). 1, 2, 3
• This occurs when the myometrium fails to contract effectively after placental delivery, preventing occlusion of uterine blood vessels at the placental bed. 2, 4
• Atony presents clinically as a soft, boggy uterus that fails to contract properly on palpation. 5

Genital Tract Lacerations (Second Most Common)

• Trauma-related hemorrhage from lacerations, uterine rupture, or incision extensions is the second leading cause. 1
• Important clinical distinction: When PPH occurs with a firm, well-contracted uterus, genital tract trauma becomes the leading cause in that specific scenario, as atony is effectively ruled out. 5
• Vaginal tears and episiotomy sites can be identified through direct visual inspection. 1, 5

Retained Products of Conception

• RPOC complicates approximately 1% of third-trimester deliveries and is the second most common etiology for PPH after uterine atony overall. 1
• However, RPOC is typically seen in delayed PPH rather than immediate postpartum bleeding. 1

Bleeding Disorders (Least Common)

• Coagulopathy, whether inherited or acute (related to conditions like amniotic fluid embolism, placental abruption, severe pre-eclampsia, or HELLP syndrome), is less common but potentially life-threatening. 1
• Hypofibrinogenemia occurs in only 17% of cases with blood loss exceeding 2000 mL. 6

Clinical Approach Algorithm

When evaluating postpartum hemorrhage after SVD, follow this systematic assessment (the "Four T's" mnemonic): 7

1. Tone (Atony) - Assess uterine firmness first; if soft and boggy, diagnose atony
2. Trauma (Lacerations) - If uterus is firm, thoroughly inspect genital tract for lacerations
3. Tissue (RPOC) - Verify complete placental delivery
4. Thrombin (Coagulopathy) - Assess for bleeding disorders if other causes excluded

Common Pitfall

Do not assume genital tract laceration is the primary cause simply because bleeding occurs after SVD. While lacerations are common after vaginal delivery, uterine atony remains statistically the most frequent cause of significant hemorrhage, accounting for 3-4 times more cases than trauma. 1, 3