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Women on Oral Contraceptives

Nov 2008 – by N. Santoro, MD

A 37 year old woman, G2P2, who has a BMI of 23 kg/m2, is taking hormonal contraception and is scheduled for a cholecystectomy. She requests instructions on stopping her oral contraceptive pills pre-operatively.

Several features increase a woman's risk of a VTE event. These include hormonal contraception and immobilization. Exogenous estrogen, particularly oral estrogen, increases risk by 3-5 fold, with higher doses of estrogen conferring increased risk5,6. Venous thromboembolism attributed to birth control pill use has been estimated to occur at a rate of 3/10,000/year7. Perioperative deep vein thrombosis (DVT) is detected about twice as often in women who use oral contraceptives than in those who do not in the few studies that have performed such comparisons5. For this reason, it has been recommended that hormones be discontinued prior to surgical procedures that will require immobilization. In a menopausal woman, discontinuation of hormones would be a relatively simple clinical decision, since the potential for pregnancy no longer exists and the older age of women at menopause puts them at overall higher risk for DVT. A waiting period of 6 weeks is optimal, since it allows liver-induced clotting factors to normalize5. In the absence of the luxury of such a waiting period, hormones should be discontinued as soon as the clinician is aware of the need for the surgical intervention.

Women who discontinue oral contraceptives will be at risk for pregnancy unless they adopt a new method immediately. This is not always practical or possible. For highly motivated patients who understand the need to use back-up contraception, discontinuing the oral contraceptives poses little short term risk. On the other hand, for many less-than-perfectly adherent patients there is a real risk of an unintended pregnancy if they discontinue oral contraceptives7. For such patients, consideration of a switch to an intrauterine method of contraception prior to the elective surgery may be an alternative. The 'judgment call' of whether or not to stop the oral contraceptives will rely on the assessment of the patient and her physician about the likelihood of an unintended pregnancy versus the increased risk of a VTE.

Others have recommended VTE prophylaxis with low dose anticoagulation in lieu of discontinuation of the oral contraceptives. While this idea is attractive, there are significant complications associated with anticoagulation, including increased operative blood loss and spontaneous hemorrhage. Given the very low rate of VTE in healthy young women with no risk factors beyond the use of hormonal contraception, it is difficult to justify the risk unless the planned surgery is prolonged and there is a lengthy period of immobilization anticipated postoperatively8.

VTE prophylaxis should always include the use of calf compression stockings, even for a woman in this low-risk age group with a low risk profile. Pneumatic massage devices can also be used.

It is NOT indicated to perform a thrombophilia workup in a clinical setting such as this.

5. Sue-Ling H, Hughes LE. Should the pill be stopped preoperatively? British medical journal (Clinical researched 1988;296(6620):447-8.
6. Vessey MP. Thrombosis and the Pill. Prescribers' journal 1970;10(1):1-7.
7. Pymar HC, Creinin MD. The risks of oral contraceptive pills. Seminars in reproductive medicine 2001;19(4):305-12.
8. ACOG Practice Bulletin 84, August 2007. Prevention of deep vein thrombosis and pulmonary embolism.