What are the primary causes of postpartum hemorrhage?

Causes of Postpartum Hemorrhage

The primary cause of postpartum hemorrhage is uterine atony, accounting for approximately 70% of cases, followed by genital tract trauma, retained placenta, abnormal placentation, and coagulopathy. 1, 2

Primary Causes of PPH

The causes of postpartum hemorrhage can be systematically organized using the "Four T's" mnemonic, which addresses the four most common etiologies 3:

Tone (Uterine Atony) - Most Common

• Uterine atony is responsible for 70.6% of all PPH cases and represents the failure of effective uterine contraction after delivery 2
• This is typically a clinical diagnosis in more than 75% of patients 1
• Uterine atony is the leading cause of both primary and secondary PPH 4, 5

Trauma (Genital Tract Injury)

• Genital tract trauma accounts for 16.9% of PPH cases 2
• This category includes:
  • Lower genital tract lacerations with palpable perineal or vaginal hematomas 1
  • Bladder flap hematoma 1
  • Subfascial/prevesical hematoma (secondary to epigastric vessel injury or direct tear of the rectus muscle) 1
  • Uterine rupture/scar dehiscence 1
  • Iatrogenic trauma from cesarean delivery or episiotomy 5

Tissue (Retained Products/Placental Disorders)

• Retained placenta accounts for 16.4% of PPH cases 2
• Retained products of conception (RPOC) complicate approximately 1% of third trimester deliveries and represent the second most common etiology after uterine atony, particularly in delayed PPH 1
• Abnormal placentation (placenta accreta spectrum) accounts for 3.9% of cases 2
• Vascular uterine anomalies (VUA) representing subinvolution of the placental bed may be associated with RPOC 1

Thrombin (Coagulopathy)

• Coagulopathy accounts for 2.7% of PPH cases 2
• This includes inherited coagulopathies or acute conditions related to:
  • Amniotic fluid embolism 1
  • Placental abruption 1
  • Severe pre-eclampsia or HELLP syndrome 1
• Hypofibrinogenemia is a predictor of severe hemorrhage 4

Temporal Classification

Primary (Early) PPH

• Occurs within the first 24 hours after delivery 1
• Most commonly caused by uterine atony, lower genital tract laceration, and coagulopathy 1

Secondary (Late/Delayed) PPH

• Occurs from 24 hours to 6 weeks postpartum 1
• Causes include uterine atony, vascular uterine anomalies, placental attachment disorders, and rarely gestational trophoblastic disease 1

Multiple Concurrent Causes

Approximately 7.8% of women with PPH have multiple concurrent causes, which supports the use of treatment bundles rather than single-intervention approaches 2. This finding emphasizes that clinicians must systematically evaluate all four categories (Tone, Trauma, Tissue, Thrombin) rather than stopping after identifying one cause 3.

Clinical Significance

PPH is among the top three causes of maternal death in the United States and accounts for 27% of all maternal deaths worldwide 1. It affects 1% to 5% of all deliveries and may be life-threatening 1. The condition is defined as any hemorrhage associated with signs or symptoms of hypovolemia within 24 hours of delivery, regardless of delivery type 1.