Body Mass Index, Surgery, and Risk of Venous Thromboembolism in Middle-Aged Women: A Cohort Study

Study Questions:

Does obesity independently influence risk for venous thromboembolism (VTE) around the time of surgery?


Questionnaire data from the Million Women Study were linked to hospital admission and death records. Women were recruited between 1996 and 2001 through the National Health Service Breast Screening Program in England and Scotland, and were followed for an average of 6 years. Women completed a questionnaire, which included information on weight, height, use of hormone therapies (including oral contraceptive use), smoking status, physical activity, alcohol consumption, medical and reproductive history, and educational attainment. Women with a prior history of VTE, clotting disorders, cancer, or surgery within 12 weeks of recruitment were excluded. The primary outcome was VTE.


A total of 1,170,495 women (mean age 65 years) were included in the National Health Screening program. During the follow-up period, 6,438 were admitted to the hospital or died from VTE. Body mass index (BMI) distributions included: 46.8% of participants were a normal weight or less (BMI <25 kg/m2), 35.7% were overweight (BMI 25-29.9 kg/m2), and 17.5% were obese (BMI >30 kg/m2). After adjustment for potential confounders, the relative risk (RR) of VTE increased with increasing BMI. Women with a BMI ≥35 kg/m2 were 3-4 times as likely to develop VTE as those with a BMI 22.5-24.9 (RR, 3.45; 95% confidence interval, 3.09-3.86). Overweight and obese women were more likely than lean women to be admitted for surgery and also to develop postoperative VTE. During a 12-week period without surgery, the incidence rates of VTE per 1,000 women with a BMI <25 and ≥25 were 0.10 (0.09-0.10) and 0.19 (0.18-0.20), respectively. The corresponding rates in the 12 weeks following day and inpatient surgery were respectively, about 4 and 40 times higher.


The investigators concluded that BMI is positively associated with risk for VTE, and this risk is greater after surgery than without surgery.


These data suggest a significant increased risk of VTE among overweight and obese women undergoing surgery. Prevention VTE is often overlooked; however, quality metrics and system change are warranted to reduce VTE risk, particularly among overweight/obese patients.

Clinical Topics: Prevention, Pulmonary Hypertension and Venous Thromboembolism, Vascular Medicine, Smoking

Keywords: Neoplasms, Contraceptives, Oral, Overweight, Scotland, Venous Thromboembolism, Smoking, Ubiquitin-Protein Ligases, Body Mass Index, Motor Activity, Cardiovascular Diseases, Obesity, England

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