Risk of cerebral venous thrombosis increased amongst women on oral contraceptives

1. In this unmatched case-control study, risk of cerebral venous thrombosis (CVT) amongst women on oral contraceptives increased in a dose-dependent manner depending on their BMI category (normal, overweight, or obese).

2. There was no statistically significant association between BMI and CVT in males or in women who did not use contraceptive pills. While obesity amongst women was not an independent risk, it perhaps had an additive effect when combined with oral contraceptives.

Evidence Rating Level: 3 (Average)

Study Rundown: It is well known that obesity is associated with increased thrombosis risk, including pulmonary embolism and deep vein thrombosis. However, studies have not assessed the relationship between cerebral venous thrombosis (CVT) and obesity in adults. Established risk factors for CVT include oral contraceptive pill (OCP) use and cancer. This study assessed whether obesity was also a risk factor for CVT.

Based on this unmatched case-control study, risk of cerebral venous thrombosis (CVT) amongst women on oral contraceptives increased in a dose-dependent manner depending on their BMI category (normal, overweight, or obese). There was no significant association with increasing BMI and CVT in women who did not use OCP or amongst men. While obesity amongst women was not an independent risk, it perhaps had an additive effect when combined with oral contraceptives. Strengths of this study included assessment of previously unstudied risk factor for CVT. Limitations of this study included study design (unmatched case-control study), in which causation could not be determined. Increased BMI could have been a confounder, so further analysis would be necessary to determine the role of obesity and CVT.

Click to read the study, published today JAMA Neurology

Relevant Reading: Case-control study of risk of cerebral sinus thrombosis in oral contraceptive users and in carriers of hereditary prothrombotic conditions.

In-Depth [case-control study]: This unmatched case-control study identified cases from July 2006 to October 2009 in the Netherlands. Controls were recruited from March 1999 to September 2004. Cases were patients with confirmed CVT from two prospective cohorts in the Netherlands. Risk factor and exposure information collection was determined through standardized case report forms for cases and through self-reported questionnaires for controls. Body mass index categories were as follows: normal BMI <25, overweight BMI 25 to 29.99, and obese BMI ≥30.

The final study population included 186 cases of CVT and 6134 controls. Cases were on average younger, more often female, more often used OCPs, more frequently had a history of cancer. Initial analysis showed that patients with CVT were more likely to be obese (adjusted OR 2.63; 95%CI 1.53-4.54). When stratified by sex, there was no association between obesity and risk of CVT amongst men (aOR 1.16, 95%CI 0.25-5.30). However, women, if either overweight or obese, were associated with CVT (aOR 1.71, 95%CI 1.01-2.91 and aOR 3.50, 95%CI 2.00-6.14, respectively). When further stratified by women and OCP usage, there was no association between CVT and BMI in women who did not use OCP (aOR 1.29, 95%CI 0.46-3.66 in women with BMI ≥ 30). However, amongst women who used OCP, there was an increased risk of CVT across all BMIs, including normal (aOR 5.09, 95%CI 2.58-10.02), overweight (aOR 11.8, 95%CI 5.94-23.74), and obese (aOR 29.26, 95%CI 13.47-63.60). It is unclear if obesity has an interaction with OCPs or is a confounder in this association.

Image: PD

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