Grand Rounds

What impact does Pre-pregnancy BMI have on Venous Thromboembolism Risk?

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

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

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)

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

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