Re: Venous thrombosis in users of non-oral hormonal contraception: follow-up study, Denmark 2001-10
I would certainly have been disappointed if Samuel Shapiro (SS) had not made a response to our latest publication, just as he has to all of our other recent articles on hormonal contraception. I had perhaps expected at least a single new critique, rather than just repetition of arguments which I have previously refuted.
But, again, the assumption that all users of the Patch and NuvaRing® are new users, and that all users of combined oral contraceptives (COC) are not, is contradicted by the data. Many users of patch and of NuvaRing® were switchers, and thus also long term users. And many users of COC with levonorgestrel were new users. The important thing is that we had detailed information about use of all hormonal contraceptive products over a 15-year long period. Therefore we were able effectively to adjust for length of use in our analysis, ensuring that we compared equal length of use with equal length of use for different product groups.
If SS’ repeated claims were true, that our results are due to bias caused by our comparison of long-term users of COC with levonorgestrel to short term users of, in this case NuvaRing® and the Patch, then we should also find a low risk of thrombosis for COC with the third generation progestogens desogestrel and gestodene. What we see now, however, more than 20 years after launch, is that users of third generation COC still have double the risk of venous thrombosis as compared to users of COC with levonorgestrel. This doubling of the rate of venous thrombotic events is the same risk as conferred by the new NuvaRing®.
An incidence rate of 2 per 10 000 women years for confirmed first time venous thrombosis in non-pregnant non-users of hormonal contraception, without previous or current cancer, is quite in agreement with previous studies. Higher published estimates in other studies typically include non-confirmed events, recurrent episodes, events in pregnant or puerperal women, events in women with previous or current cancer, or events in women using hormonal contraception.
The other points made by SS have been thoroughly dealt with in our previous response to Dinger and SS, to which we refer (1). The response can also be downloaded as pdf from the link.
1. Repy to critique by Jürgen Dinger and Samuel Shapiro. Part I-III. BMJ 2011, December 7, http://www.bmj.com/content/343/bmj.d6423?tab=responses
Competing interests: The author has within the last three years received honoraria for speeches in pharmacoepidemiological issues, including fees from Bayer Pharma Denmark, MSD Denmark, and Theramex, Monaco, and has been expert witness for plaintiff in a legal US case in 2011.