BACKGROUND AND PURPOSE: 

• The most common cause of postpartum hemorrhage (PPH) is uterine atony 
• Several risk assessment tools, recognized by professional bodies, are used for PPH but have moderate predictive value 
  • “This limitation may be partly due to the tools’ development via expert consensus opinion and a lack of systematically reviewed evidence to support or refute the included risk factors” 
• Ende et al. (Obstetrics & Gynecology, 2021) sought to identify and quantify the risk factors for atonic PPH 

METHODS: 

• Systematic review and meta-analysis 
• Inclusion criteria 
  • RCTs, prospective or retrospective cohort studies, and case-control studies 
  • Studies of pregnant patients who developed atonic PPH and reported at least one risk factor 
• Study design 
  • Low and moderate risk of bias studies 
    • Qualitative synthesis: Each risk factor was classified as definite, likely, unclear, or not a risk factor 
    • Quantitative meta-analysis: Used for risk factors with homogenous definitions and references ranges 
• Primary outcome 
  • Risk factors associated specifically with atonic PPH 

RESULTS: 

• 27 studies 
• There were 47 potential risk factors for atonic PPH that were identified 
  • 6 definite risk factors  
    • Asian race  
    • Prior postpartum hemorrhage 
    • Preexisting or gestational diabetes mellitus 
    • Placental disorders 
    • Prolonged labor 
    • Genital tract trauma sustained during delivery 
  • 9 likely risk factors 
    • Hispanic ethnicity 
    • Nulliparity 
    • Hypertensive diseases of pregnancy 
    • Multiple gestation 
    • Chorioamnionitis 
    • Uterine rupture 
    • Predelivery oxytocin exposure 
    • Induction of labor 
    • Instrumented vaginal delivery 
  • The remaining 32 assessed risk factors, including obesity and magnesium exposure, were not associated with atonic PPH or had conflicting or unclear evidence 

CONCLUSION: 

• Many risk factors for atonic postpartum hemorrhage are included in current risk-assessment tools 
• Factors with the greatest impact included prior PPH, placenta previa, placental abruption, uterine rupture, and multiple gestation 
• Novel risk factors included hypertension, diabetes, and ethnicity 
• Obesity and magnesium exposure were not associated with atonic PPH 

The authors conclude:

By more narrowly defining our focus to only atonic postpartum hemorrhage, we aimed to provide more definitive evidence supporting or refuting presumed risk factors, given that each etiology of postpartum hemorrhage likely has a unique set of contributing factors 

Ende et al. (Obstetrics & Gynecology, 2021)

These findings should lead researchers and clinicians to refine current risk-assessment tools further 

Learn More – Primary Sources: 

Risk Factors for Atonic Postpartum Hemorrhage: A Systematic Review and Meta-analysis 

Related ObG Topics:

Does ART Increase Risk of Postpartum Hemorrhage?

Does Time of Day Impact Postpartum Hemorrhage Outcomes?

Mild Thrombocytopenia: Is it a Risk Factor for Postpartum Hemorrhage?

Results From the Landmark Trial on Tranexamic Acid for Postpartum Hemorrhage