CAVEATS
A cohort study, no contraceptive start date, and incomplete tobacco use data
This is an observational cohort study, so it is subject to confounding factors and biases. It does, however, include a very large population, which improves validity. The study did not account for COC start date, which may be confounding because the risk of VTE is highest in the first 3 months to one year of COC use.12 Data on tobacco use, a significant independent risk factor for arterial but not VTE, was incomplete, but in other studies has only marginally affected outcomes.3,13
CHALLENGES TO IMPLEMENTATION
Low-dose estrogen is associated with increased vaginal spotting
One potential challenge to implementing this practice changer may be the increased rate of vaginal spotting associated with low-dose estrogen. COCs containing 20 mcg of estrogen are associated with spotting in approximately two-thirds of menstrual cycles over the course of a year.14 That said, women may prefer to endure the spotting in light of the improved safety profile of a lower-dose estrogen pill.
ACKNOWLEDGEMENT
The PURLs Surveillance System was supported in part by Grant Number UL1RR024999 from the National Center For Research Resources, a Clinical Translational Science Award to the University of Chicago. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center For Research Resources or the National Institutes of Health.
