This study from the Journal of OB-GYN: Canada was the first population based study that used a more accurate method of measuring the risk of pregnancy.
The full study is available here. The results are as I would expect: the effectiveness of Plan B is "markedly lower" than previously reported. I'll let the study speak for itself:
When the data for all women are combined, the mean risk of pregnancy is estimated to be 4.12% (95% CI 3.77–4.49). This risk of pregnancy is substantially lower than that estimated in studies comparing the effectiveness of the levonorgestrel and Yuzpe regimens.3,4
This is the first report of risk of pregnancy among a population-based cohort of women requesting EC from pharmacists under conditions of routine use. Overall, in the two groups combined, the estimated risk of pregnancy was 4.12%, which is markedly lower than that reported when effectiveness of EC has been estimated in clinical trials.2–5
If the estimates of risk of pregnancy from the present study and related studies are reasonably accurate, the effectiveness of EC among women in the general population may be markedly lower than is currently believed by professionals and advocates for wider EC use. In light of these observations, consideration should be given to revising the information on effectiveness that physicians, pharmacists and other health care professionals provide to women seeking EC.
Serge,
ReplyDeleteI'm trying to crunch the numbers to figure out what the effectiveness of EC would have been estimated at if the WHO used the pregnancy risk number from the Canadian study.
Correct me if I'm wrong but my estimations from trying to decipher how they figured out the effectiveness (is it percentage of pregnancies divided by pregnancy risk?) show that if the WHO study used the pregnancy risk number (4.12) from the Canadian study instead of the 7.7 garnered from the traditional method of estimating pregnancy risk and then took the percentage of women who became pregnant from the WHO study then the effectiveness of EC would be somewhere around 75% and not the 85% cited for the WHO.