Combined hormonal contraception raises the risk for venous thromboembolism fivefold overall, with certain formulations increasing that risk even further and with thrombophilic genotypes raising it further still, according to a report published online Aug. 5 in Obstetrics & Gynecology.
To assess the association between various types of hormonal contraception and venous thromboembolism (VTE) risk, Swedish investigators performed a nationwide case-control study involving 948 women aged 18-54 years who were treated for deep vein thrombosis of the leg or pelvis, pulmonary embolism, or both conditions during a 6-year period and 902 healthy control subjects from the general population. All the women provided a blood sample for genetic analysis and provided detailed information regarding their contraceptive use, body mass index (BMI), smoking status, and recent history of immobilization, said Dr. Annica Bergendal of the Centre for Pharmacoepidemiology, Karolinska Institutet, Stockholm, and her associates.
A total of 32.8% of the case group reported current use of combined hormonal contraception, compared with only 11.9% of the control group. Overall, current use of combined hormonal contraception was associated with a fivefold increased risk of VTE, with an adjusted OR of 5.3. "Combinations with the progestogen desogestrel yielded the highest risk estimate (adjusted OR, 11.4), followed by drospirenone (adjusted OR, 8.4). The adjusted OR could not be calculated for lynestrenol because there were no exposed women in the control group," the investigators wrote (Obstet. Gynecol. 2014;124:600-9).
In contrast, progestogen-only contraception did not increase the risk of VTE, except at the highest dose level.
Women who used combination contraception and were carriers of factor V Leiden or of the prothrombin gene mutation were at extremely high risk for VTE, nearly 20-fold for either, compared with nonusers and noncarriers. Women who used combination contraception and were carriers of factor XIII had a much lower, but still elevated, risk for VTE (OR, 2.8).
All of these differences in risk appeared to be independent of BMI, smoking status, and recent history of immobilization, Dr. Bergendal and her associates added.
This study was supported by unrestricted grants from Janssen-Cilag, Novartis, Organon, Schering, Wyeth, AFA Insurance, and the Medical Products Agency. Dr. Bergendal and her associates reported no relevant financial conflicts.