Coagulation

VTE risk slightly higher with extended and continuous oral contraception


Venous thromboembolism (VTE) risk is slightly higher for women using extended- and continuous-cycle combined oral contraceptive (COC) regimens but the difference may not be clinically significant, US research suggests.

With many women opting for extended cycles of 84/7 days or 365/0 days of COC use in place of the traditional 21/7 Pill cycle, epidemiologists at the FDA decided to investigate whether the exposure to higher cumulative doses of oestrogen was associated with an increased risk of VTE.

In a retrospective cohort study they compared the rates of VTE hospitalisation for 210,691 women who started using extended or continuous COCs and 522,316 women who started using traditional cyclic COCs, while keeping the progestogen type constant.

Their analysis, published in JAMA Internal Medicine, found that the incidence rates for VTE were 1.54/1000 person years for women using extended/continuous COCs, and 0.83 for women using cyclic COCs (Hazard Ratio 1.84).

After adjusting for confounding factors such as age and baseline cardiovascular risks, the propensity score-matched incidence rates for VTE showed less discrepancy (1.44 vs 1.09 for extended/continuous vs cyclic COCs), and the Hazard Ratio for VTE was reduced to 1.32.

The authors of the study, from the FDA’s Division of Epidemiology, said the absolute difference in incidence rates of 0.35/1000 person years was small and may not translate into a clinically significant risk difference for VTE between cyclic and extended/continuous cycle COCs

In subgroup analysis, the overall VTE risks and differences in incidence rates between cyclic and non-cyclic COC regimens were greater among older women (2.47 vs 1.76/1000 person years for women aged 35-50), and also for women using continuous COCs only (2.47 vs 1.64/100 person years) compared to cyclic COCs.

The investigators noted that theirs was the first major study to look at the rates of VTE according to COC cycle rather than progestogen type.

“We did not see strong evidence supporting a VTE risk difference,” they concluded.

“Accordingly, we do not recommend selective prescribing of COCs based on the cyclic and continuous/extended type. Clinicians should prescribe COCs based on patients’ individual risk factors and preferences.”

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