Causes of Postpartum Hemorrhage
Uterine atony is the leading cause of postpartum hemorrhage, 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")
1. Tone (Uterine Atony) - 70.6% of cases
- Failure of the uterus to contract effectively after delivery
- Most common cause diagnosed clinically in >75% of patients
- Initially responds to uterine massage and oxytocin in most cases 1, 2
2. Trauma - 16.9% of cases
- Lower genital tract lacerations with palpable perineal or vaginal hematomas
- Uterine rupture or scar dehiscence (particularly after cesarean delivery)
- Bladder flap hematoma or subfascial/prevesical hematoma from epigastric vessel injury
- Direct tears of the rectus muscle
- Episiotomy-related bleeding 1, 3
3. Tissue - 16.4% of cases
- Retained products of conception (RPOC) with or without superimposed infection
- Complicates approximately 1% of third trimester deliveries
- Second most common etiology after uterine atony, typically seen in delayed PPH
- Adherent placenta (placenta accreta spectrum disorders)
- Uterine inversion 1, 2
4. Thrombin (Coagulopathy) - 2.7% of cases
- Inherited coagulopathies
- Acute coagulopathy related to:
Additional Causes Requiring Imaging Diagnosis
Vascular Uterine Anomalies (VUA)
- Represent subinvolution of the placental bed
- May be associated with RPOC
- Increased risk of significant PPH when peak systolic velocity >83 cm/s
- Usually resolve with RPOC removal or expectant management 1
Hematomas
- Bladder flap hematoma (>5 cm raises suspicion for uterine dehiscence)
- Subfascial/prevesical hematoma (small <4 cm may not be clinically significant)
- Perivaginal space hematoma 1
Multiple Concurrent Causes
7.8% of women have multiple simultaneous causes of PPH, supporting the use of treatment bundles rather than single interventions 2
Timing Classification
Primary (Early) PPH - Within first 24 hours
- Predominantly uterine atony
- Trauma-related causes
- Acute coagulopathy 1
Secondary (Late/Delayed) PPH - 24 hours to 6 weeks
- Uterine atony
- Vascular uterine anomalies
- Placental attachment disorders
- Rarely gestational trophoblastic disease 1
Clinical Pitfall
Multiple causes often coexist in the same patient. Do not stop investigating after identifying one cause if bleeding persists despite appropriate treatment. The presence of uterine atony does not exclude concurrent trauma, retained tissue, or coagulopathy 2, 3.