03.15.2016

Explain risk and discuss nonhormonal contraception

by Kay Jackson
Contributing Writer, MedPage Today

Women who are overweight or obese and using oral contraceptives had a significantly increased risk of cerebral venous thrombosis (CVT) compared with women of normal weight not taking oral contraceptives, an unmatched case-control study showed.

Overweight and obesity were associated with an increased risk of CVT in a dose-dependent manner, according to Jonathan M. Coutinho, MD, PhD, of the Academic Medical Center in Amsterdam, and colleagues, writing online in JAMA Neurology.

Women who were overweight (BMI 25-29.9) had a markedly higher risk of CVT (adjusted odds ratio 11.87, 95% CI 5.94-23.74) while those who were obese (BMI 30 and above) had an even more dramatic increase in risk (adjusted OR 29.26, 95% CI 13.47-63.60).

But, in the absence of oral contraceptive use, no association was found between overweight or obesity and CVT in women (adjusted OR 0.85 for overweight, 95% CI 0.30-2.41; adjusted OR 1.29 for obesity, 95% CI 0.46-3.66). Excess weight also did not seem to be a factor in CVT risk for men.

“To our knowledge, this is the first case-control study that examined the association between obesity and CVT,” wrote the study authors. “Our results suggest that obesity is associated with a substantially increased risk of CVT in women who use oral contraceptives. This increased risk should be taken into consideration when prescribing oral contraceptives to obese women.”

Conversely, the increased risk of CVT should not be taken as a reason not to prescribe oral contraceptives in this patient population, emphasized Coutinho and colleagues. They pointed out that while the relative risks are substantially increased, the absolute risk of CVT remains small. (The current study involved 186 cases of CVT seen in two large European cities during more than 5 years.)

What’s more, not prescribing oral contraceptives could result in pregnancy and pregnancy-related thrombosis, they pointed out. Consequently, the researchers said, the best advice for women with a BMI of 25 or more who are using contraceptives is to tell them of the risks associated with oral hormonal products and suggest alternative methods.

“These findings are novel and in concordance with prior studies on obesity and oral contraceptive use as risk factors for venous thromboembolism (VTE),” Chirantan Banerjee, MD, MPH, of the Medical University of South Carolina in Charleston, commented in an accompanying editorial.

“Given the lack of prospective data thus far, this is an important study because of the use of appropriate controls, predefined confounders, and appropriate subgroups,” Banerjee said.

Prospective studies are needed to corroborate and validate these findings, he added.

In spite of the increased relative risk of CVT in overweight and obese women taking oral contraceptives, the absolute risk of CVT in obese women taking OCs remains low and should not preclude the use of oral contraceptives in this group, Banerjee agreed. Better counselling and education of this patient population, along with consideration of alternate nonhormonal OC options, would be “prudent,” he said.

The case-control study included 186 cases and 6,134 healthy controls. Cases were consecutive adults patients with CVT included in two prospective cohorts admitted from July 2006 through December 2014 to the Academic Medical Center in Amsterdam or from October 2009 to December 2014 at Inselspital University Hospital in Berne, Switzerland.

The control group was made up of healthy participants from a Dutch case-control study which assessed risk factors for deep vein thrombosis and pulmonary embolism (Multiple Environmental and Genetic Assessment of Risk Factors for Venous Thrombosis), performed from March 1, 1999, to Sept. 31, 2004, and data analysis was performed in early 2015.

The investigators adjusted for sex, age, history of cancer, ethnicity, smoking status, and oral contraceptive use.

When compared with controls, cases tended to be younger with a median age of 40 versus 48 years. They also more often had history of cancer (9.1% versus 3.8%).

Banerjee noted some limitations of the study, including the small number of women who did not use oral contraceptives, the use of unmatched historical controls, and the lack of BMI data for some of the cases.

• Reviewed by F. Perry Wilson, MD, MSCEAssistant Professor, Section of Nephrology, Yale School of Medicine and Dorothy Caputo, MA, BSN, RN, Nurse Planner

LAST UPDATED 03.15.2016