Obesity Considered a Risk Factor for CVST in Women Taking Birth Control

March 22nd 2016

Nurse practitioners and physician assistants should inform obese or overweight women taking oral contraceptives that they face an increased risk for cerebral venous thrombosis.

Nurse practitioners and physician assistants should inform obese or overweight women taking oral contraceptives that they face an increased risk for cerebral venous sinus thrombosis (CVST).

A new study inJAMA Neurologyrecently examined 186 patients with CVST admitted to medical centers and hospitals between 2006 and 2014. The control group totaling 6134 patients was made up of healthy individuals from the control population of the Multiple Environmental and Genetic Assessment of Risk Factors for Venous Thrombosis study, which analyzed patients from 1999 to 2004. In this study, risk factors for deep vein thrombosis and pulmonary embolism were examined.

It is already known that obesity is a risk factor for deep vein thrombosis of the leg and pulmonary embolism. However, the researchers behind the new study sought to determine whether there is an association between obesity and CVST. To their knowledge, one had not been assessed before.

They considered the study subjects to be obese if they had a body mass index (BMI) ≥30, and patients were considered overweight if they had a BMI between 25 and 29.99.

The researchers adjusted for sex, age, history of cancer, ethnicity, smoking status, and use of oral contraceptives. The study subjects had a younger median age than the control group (40 years vs 48 years, respectively), were more often female (71.5% vs 52.5%), used oral contraceptives more often (72.9% vs 23.5%), and had more histories of cancer (9.1% vs 3.8%).

The researchers found that obesity was linked with an almost 30-fold increased risk of CVST compared with women of a normal weight who did not use oral contraceptives. Notably, no such link was found in women (and men) who did not use oral contraceptives.

“Although the relative risks are increased substantially, the absolute risks of [CVST] are small. Moreover, withholding oral contraceptives may lead to an increase in unintended pregnancies and thus the number of pregnancy-related thrombosis cases,” the study authors concluded. “Nevertheless, obese women should be informed about the increased risk of thrombosis if they use oral contraceptives, especially if other risk factors are present.”

The researchers noted that one possible way obesity may increase patients’ risk of thrombosis is through changes in coagulation factor levels. Obese women are more likely to have higher plasma concentrations of prothrombotic factors, and obesity is also associated with increased activated protein C resistance and higher concentrations of factor VIII, which are risk factors for thrombosis. In addition, oral contraceptives results in increased activated protein C resistance.

The study authors stated that these results could make health care providers hesitant to prescribe oral contraceptives to obese women. However, they emphasized that the important thing is to inform patients of the risks and consider prescribing alternative methods of contraception, such as intrauterine devices.

In terms of study limitations, the researchers pointed out that they could only include a small number of patients with CVST, especially those with CVST who did not take oral contraceptives.

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