BACKGROUND AND PURPOSE:

• Obesity is a well-known risk factor for venous thromboembolism (VTE)
• Butwick et al. (BJOG 2018) assessed the relationship between pre-pregnancy BMI and pregnancy-related VTE

METHODS:

• Population-based cohort study
  • Women age 15 to 50 years
  • Singleton pregnancies
  • Delivered in any California hospital (2008 – 2012)
• Primary exposure: Pre-pregnancy BMI
  • Categorized using WHO classification (see ‘Related ObG Topics’ below)
• Determined pre-pregnancy BMI and presence of
  • Antepartum VTE | Postpartum (up to 9 months) VTE (delivery VTE also assessed, but due to low ‘n’, multivariate analysis could not be performed)
• Association of BMI and risk of VTE was examined using logistic regression, with normal BMI as reference

RESULTS:

• 2,449,133 women were included
• Overall prevalence of VTE
  • Antepartum: 0.04%
  • Delivery: 0.01%
  • Postpartum: 0.04%

Prevalence of antepartum and postpartum VTE increased with higher BMI

• Antepartum VTE (P < 0.001)
  • Underweight: 2.3/10,000
  • Normal BMI: 3.0/10,000
  • Overweight: 3.8/10,000
  • Obesity class I: 4.2/10,000
  • Obesity class II: 4.7/10,000
  • Obesity class III: 10.6/10,000
• Postpartum VTE (P < 0.01)
  • Underweight: 2.0/10,000
  • Normal BMI: 3.1/10,000
  • Overweight: 3.9/10,000
  • Obesity class I: 5.6/10,000
  • Obesity class II: 9.0/10,000
  • Obesity class III: 13.2/10,000
• Obesity class III women had highest risk of pregnancy-related VTE compared to normal BMI women
  • Antepartum VTE:  Adjusted odds ratio (OR) 2.9 (95% CI, 2.2–3.8)
  • Postpartum VTE:  aOR 3.6; (95% CI 2.9–4.6)

CONCLUSION:

• Strong ‘dose response’ effects between pre-pregnancy BMI with antepartum and postpartum VTE
• Obesity class III should be considered a ‘major risk factor’ for antepartum and postpartum VTE and may inform future guideline considerations

Learn more – Primary Sources:

Prepregnancy maternal body mass index and venous thromboembolism: a population-based cohort study

Related ObG Topics:

Does BMI Impact Success of Vacuum-Assisted Vaginal Delivery?

Recommended Weight Gain and Obesity Management in Pregnancy

ACOG Guidance on Thrombophilia in Pregnancy

The CMQCC Toolkit: Venous Thromboembolism Prevention and Management at Delivery