What are the causes of postpartum hemorrhage (PPH)?

From the Guidelines

Postpartum hemorrhage (PPH) is most commonly caused by uterine atony, which accounts for about 70-80% of cases, followed by trauma, tissue, and thrombin disorders, as noted in the studies 1. The causes of PPH can be remembered using the "4 Ts": Tone (uterine atony), Trauma, Tissue, and Thrombin.

• Uterine atony, the failure of the uterus to contract effectively after delivery, is the most common cause, accounting for about 70-80% of cases, as stated in 1.
• Trauma includes lacerations of the birth canal, uterine rupture, and surgical incisions during cesarean delivery, as mentioned in 1.
• Tissue refers to retained placental fragments or abnormal placentation such as placenta accreta, increta, or percreta, as noted in 1.
• Thrombin disorders involve coagulation abnormalities, either pre-existing (like von Willebrand disease) or acquired during pregnancy (such as disseminated intravascular coagulation), as discussed in 1. Other risk factors include advanced maternal age, obesity, and anemia, as well as overdistended uterus (multiple gestation, polyhydramnios, macrosomia), prolonged labor, oxytocin augmentation, and previous PPH, as mentioned in the studies 1. Management depends on identifying the specific cause, with treatments ranging from uterotonic medications (oxytocin, methylergonovine, carboprost) for atony to surgical interventions for trauma or abnormal placentation, as stated in 1. The most recent and highest quality study 1 prioritizes uterine atony as the primary cause of PPH, and thus, management should focus on addressing this condition first.

From the FDA Drug Label

Overdosage with oxytocin injection (synthetic) depends essentially on uterine hyperactivity whether or not due to hypersensitivity to this agent Hyperstimulation with strong (hypertonic) or prolonged (tetanic) contractions, or a resting tone of 15 to 20 mm H2O or more between contractions can lead to tumultuous labor, uterine rupture, cervical and vaginal lacerations, postpartum hemorrhage, uteroplacental hypoperfusion and variable deceleration of fetal heart, fetal hypoxia, hypercapnia or death Maternal deaths due to hypertensive episodes, subarachnoid hemorrhage, rupture of the uterus and fetal deaths due to various causes have been reported associated with the use of parenteral oxytocic drugs for induction of labor and for augmentation in the first and second stages of labor Postpartum Hemorrhage In any event the cases reported did not require specific therapy for the elevated blood pressure. Use in patients with chorioamnionitis. During the clinical trials with carboprost tromethamine, chorioamnionitis was identified as a complication contributing to postpartum uterine atony and hemorrhage in 8/115 (7%) of cases, 3 of which failed to respond to carboprost tromethamine

The causes of postpartum hemorrhage include:

• Uterine hyperactivity due to hypersensitivity to oxytocin or other oxytocic agents
• Hyperstimulation with strong or prolonged contractions
• Uterine rupture
• Cervical and vaginal lacerations
• Uteroplacental hypoperfusion
• Chorioamnionitis, which can contribute to postpartum uterine atony and hemorrhage 2, 2, 3

From the Research

Causes of Postpartum Hemorrhage

• Uterine atony is the leading cause of postpartum hemorrhage, accounting for 70.6% of cases 4
• Genital tract trauma is another common cause, accounting for 16.9% of cases 4
• Retained placenta is also a significant cause, accounting for 16.4% of cases 4
• Abnormal placentation and coagulopathy are less common causes, accounting for 3.9% and 2.7% of cases, respectively 4
• Multiple concurrent causes of postpartum hemorrhage can occur, with a pooled rate of 7.8% 4

Risk Factors for Postpartum Hemorrhage

• Risk factors with a strong association with postpartum hemorrhage include:
  • Anaemia
  • Previous postpartum hemorrhage
  • Caesarean birth
  • Female genital mutilation
  • Sepsis
  • No antenatal care
  • Multiple pregnancy
  • Placenta praevia
  • Assisted reproductive technology use
  • Macrosomia with a birthweight of more than 4500 g
  • Shoulder dystocia 4
• Risk factors with moderate association with postpartum hemorrhage include:
  • BMI ≥30 kg/m2
  • COVID-19 infection
  • Gestational diabetes
  • Polyhydramnios
  • Pre-eclampsia
  • Antepartum haemorrhage 4
• Risk factors with weak association with postpartum hemorrhage include:
  • Black and Asian ethnicity
  • BMI 25-29·9 kg/m2
  • Asthma
  • Thrombocytopenia
  • Uterine fibroids
  • Antidepressant use
  • Induction of labour
  • Instrumental birth
  • Premature rupture of membranes 4

Prevention and Management

• Active management of the third stage of labor can reduce the incidence of postpartum hemorrhage 5
• Use of oxytocin after delivery of the anterior shoulder is an effective component of active management 5
• Routine episiotomy should be avoided to decrease blood loss and the risk of anal laceration 5
• Prompt diagnosis and treatment of postpartum hemorrhage are crucial to minimize morbidity and mortality 5, 6