What are the causes and management of spontaneous postpartum hemorrhage?

Causes of Spontaneous Postpartum Hemorrhage

Uterine atony is the leading cause of spontaneous postpartum hemorrhage, accounting for 70-80% of all cases, followed by genital tract trauma (lacerations, rupture), retained placental tissue, and coagulopathy. 1

Primary Causes (The "Four T's" Framework)

1. Tone (Uterine Atony) - Most Common

• Uterine atony causes 70.6-80% of all postpartum hemorrhage cases and is the most common cause of early PPH (within first 24 hours) 1, 2
• Presents with a soft, boggy uterus that fails to contract properly after delivery 1
• Risk factors include: advanced maternal age, prolonged labor, pre-eclampsia, maternal obesity, multiple pregnancy, birth weight >4000g, previous postpartum hemorrhage, and multiparity 3

2. Trauma (Genital Tract Injury) - Second Most Common

• Genital tract lacerations, uterine rupture, or incision extensions are the second leading cause of PPH 1
• When PPH occurs with a firm, well-contracted uterus, genital tract trauma becomes the primary cause to investigate 1
• Vaginal lacerations can be identified through careful visual inspection of the birth canal 1

3. Tissue (Retained Products of Conception)

• Retained placental tissue complicates approximately 1% of third-trimester deliveries and is the second most common etiology overall after atony 1
• Retained placenta is defined by WHO as spontaneous placental delivery occurring more than 30 minutes after fetal expulsion 4
• Ultrasound can diagnose retained products of conception 5

4. Thrombin (Coagulopathy)

• Inherited or acute coagulopathy is less common but potentially life-threatening 1
• Should be assessed if bleeding persists despite addressing tone, trauma, and tissue causes 1

Iatrogenic/Medication-Related Causes

Anticoagulation Therapy

• Women receiving therapeutic-dose LMWH have increased PPH risk: 29.6% experienced PPH after vaginal delivery compared to 17.6% of controls (OR 1.9,95% CI 1.1-3.5) 4
• Spontaneous labor in anticoagulated women carries 1.9-fold higher risk of PPH compared to planned induction 4
• The timing of last LMWH dose (<24 hours vs >24 hours before delivery) did not significantly affect PPH risk after vaginal delivery 4
• Major hemorrhage within 24 hours of delivery occurred in 1.2% of women receiving therapeutic anticoagulation 4

Clinical Diagnostic Algorithm

When evaluating postpartum hemorrhage with ≥1000 mL blood loss 1:

1. Assess uterine tone first: Is the uterus firm or boggy?

   • If boggy → uterine atony is the cause
   • If firm → proceed to step 2

2. Inspect the genital tract thoroughly for lacerations, extensions, or rupture

   • Vaginal lacerations are the most common cause when uterus is firm 1

3. Verify complete placental delivery: Examine placenta for missing cotyledons or membranes

   • Consider ultrasound if retained tissue suspected 5

4. Assess for coagulopathy if bleeding persists despite addressing above causes

   • Check coagulation studies and fibrinogen levels 1

Important Clinical Pitfalls

• PPH frequently occurs without identifiable risk factors - all obstetric units must be prepared regardless of patient risk profile 6
• Do not assume anticoagulation timing matters for vaginal delivery: Evidence shows no difference in PPH risk whether LMWH was given <24 hours or >24 hours before delivery 4
• A firm uterus effectively rules out atony - do not waste time with additional uterotonic agents when the uterus is already well-contracted; immediately inspect for trauma 1
• Bladder flap hematomas >5 cm should raise suspicion for uterine dehiscence, not just simple hematoma 5