Li J, et al. – In this study, researchers determined the risk for venous thromboembolism (VTE) with use of extended cyclic and continuous combined oral contraceptives (COCs; 84/7 or 365/0 days cycles) vs that observed with traditional cyclic COC use (21/7 days cycle), while holding the progestogen type constant (levonorgestrel). Observations suggested a small VTE risk difference, which may not translate into a clinically meaningful difference between continuous/extended and traditional cyclic COCs.

Methods

• Study participants included women aged 18-50 years at the time of initiating a study COC between May 2007 and September 2015.
• Estimation of hazard ratios of VTE overall and separately by ethinyl estradiol dose and age groups was performed using a propensity score approach and Cox proportional hazards regression models.
• The participants initiated continuous/extended or traditional cyclic COCs containing ethinyl estradiol or levonorgestrel of any dose.
• During the study follow-up, they determined the occurrence of first VTE hospitalization identified by an inpatient International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis code of 415.1, 415.1x, 453, 453.x, or 453.xx.

Results

• Continuous/extended COCs were initiated by 210,691 women and cyclic COCs by 522,316 women, with a mean of 0.7 person-years at risk among continuous/extended and cyclic users.
• Continuous/extended cyclic users displayed slightly higher baseline cardiovascular and metabolic conditions (7.2% vs 4.7%), gynecological conditions (39.7% vs 32.3%), and health services utilization than cyclic COC users.
• A decrease in the hazard ratio estimates was noted with propensity score-matching from 1.84 to 1.32 for continuous/extended use compared with cyclic COC use.
• The two propensity score-matched cohorts displayed continuously low absolute risk difference (0.27 per 1,000 persons) and the incidence rate difference (0.35 cases per 1,000 person-years), which may not translate into a clinically significant risk differences between cyclic and noncyclic estrogen use.