Women who use combined oral contraceptives (COC) without hormone-free or low-dose hormone intervals have a slightly elevated, but not statistically significant, risk of venous thromboembolism (VTE), compared with women who use cyclic COCs, according to research published in JAMA Internal Medicine.
Jie Li, PhD, from the Center for Drug Evaluation and Research, and colleagues performed a retrospective cohort study of 733,007 women aged 18-50 years in the Sentinel Distributed Database from 2007 to 2015 who received low-dose extended and continuous cycle (210,691 women; mean age, 30 years) COCs or cyclic COCs (522,316 women; mean age, 29 years). Continuous cycle COCs were defined as an 84/7 cycle or a 365/0 cycle, while cyclic COCs were 21/7 cycles.
The researchers noted some baseline differences between the two groups, with gynecologic conditions occurring in 40% of the noncyclic group, compared with 32% in the cyclic group; cardiovascular and metabolic conditions occurring in 7% of noncyclic women, compared with 5% of cyclic women; inflammatory disease occurring in 3% of noncyclic women, compared with 2% of cyclic women; and a slightly higher rate of health care services use in the noncyclic group, compared with the cyclic group.
Dr. Li and associates found 228 cases of VTE in the noncyclic group and 297 cases in the cyclic group, with an incidence rate of 1.54 (95% confidence interval, 1.34-1.74) per 1,000 person-years for noncyclic users and 0.83 (95% CI, 0.74-0.93) per 1,000 person-years for cyclic users (crude hazard ratio, 1.84; 95% CI, 1.53-2.21).
However, propensity score matching lowered the incidence rate to 1.44 (95% CI, 1.24-1.64) per 1,000 person-years for the noncyclic group and raised it to 1.09 (95% CI, 0.92-1.27) per 1,000 person-years for the cyclic group, for an adjusted hazard ratio of 1.32 (95% CI, 1.07-1.64), which does not show “strong evidence” of VTE risk based on a small absolute risk difference of 0.27 cases per 1,000 persons, the researchers said. They added that there might be residual or unmeasured confounding, perhaps for potential concurrent medication use or incompletely measured covariates.
“Accordingly, we do not recommend selective prescribing of COCs based on the cyclic and continuous/extended type,” Dr. Li and colleagues wrote. “Clinicians should prescribe COCs based on patients’ individual risk factors and preferences.”
The Sentinel Initiative is funded by a contract from the Department of Health and Human Services. The authors reported no relevant conflicts of interest.
SOURCE: Li J et al. JAMA Intern Med. 2018 Oct 1. doi: 10.1001/jamainternmed.2018.4251.