Causes of Postpartum Hemorrhage
The most common cause of postpartum hemorrhage is uterine atony, accounting for approximately 70% of cases, followed by genital tract trauma (17%), retained placenta (16%), abnormal placentation (4%), and coagulopathy (3%). 1, 2
Primary Causes (The "Four T's" Framework)
1. Tone (Uterine Atony) - 70.6% of cases
- Most frequent cause of PPH, diagnosed clinically in >75% of patients 1, 2
- Represents failure of effective uterine contraction after delivery
- Can present with focal or diffuse arterial/venous oozing within an enlarged uterus 1
- May be associated with retained products of conception or uterine inversion 1
2. Trauma - 16.9% of cases
- Lower genital tract lacerations with palpable perineal or vaginal hematomas 1
- Uterine rupture/scar dehiscence: Gas in myometrial defect extending from endometrium to parametrial tissue with hemoperitoneum suggests rupture 1
- Bladder flap hematoma: >5 cm size raises suspicion for uterine dehiscence 1
- Subfascial/prevesical hematoma: Secondary to epigastric vessel injury or direct rectus muscle tear 1
- Episiotomy and cesarean section increase trauma risk 3
3. Tissue - 16.4% of cases
- Retained products of conception (RPOC): Complicates ~1% of third-trimester deliveries, second most common cause after atony 1
- Adherent placenta/placenta accreta spectrum 1
- May present with or without superimposed infection 1
4. Thrombin (Coagulopathy) - 2.7% of cases
- Inherited or acquired bleeding disorders 1
- Acute coagulopathy related to:
- Amniotic fluid embolism
- Placental abruption
- Severe pre-eclampsia or HELLP syndrome 1
- Less common but potentially life-threatening 1
Additional Causes
Vascular Uterine Anomalies (VUA)
- Represent subinvolution of the placental bed 1
- May be associated with RPOC
- Peak systolic velocity >83 cm/s indicates increased PPH risk 1
- Can include pseudoaneurysms (restricted to myometrium, not extending to endometrium) 1
Secondary PPH Causes (24 hours to 6 weeks postpartum)
- Uterine atony (persistent) 1
- Vascular uterine anomalies 1
- Placental attachment disorders 1
- Gestational trophoblastic disease (rare) 1
- Endometritis 1
Multiple Concurrent Causes
Important caveat: 7.8% of women have multiple simultaneous causes of PPH 2. This finding supports using treatment bundles rather than addressing single etiologies sequentially.
Clinical Distinction: Primary vs Secondary PPH
- Primary/Early PPH: Within first 24 hours of delivery 1
- Secondary/Late/Delayed PPH: After 24 hours up to 6-12 weeks postpartum 1, 4
The definition applies to pregnancies delivered beyond 20 weeks gestation but may include hemorrhage post-terminations or early pregnancy loss 1.
Key Clinical Pitfalls
- Uterine atony is primarily a clinical diagnosis—imaging is reserved for unclear cases or when conservative measures fail 1
- RPOC can be difficult to differentiate from blood products even on multiphase CT 1
- Enhanced myometrial vascularity (EMV) may represent normal physiologic reversion rather than pathologic AVM—avoid overdiagnosis 4
- Multiple causes often coexist—maintain high suspicion and address all potential etiologies 2