Evaluating Pregnancy Rates in Fertility Awareness-Based Methods for Family Planning: Simulated Comparison of Correct Use to Avoid, Method-Related, and Total Pregnancy Rates.

Abstract

Fertility awareness-based methods (FABMs) can be used by couples to avoid pregnancy, by avoiding intercourse on fertile days. Users want to know what the highest effectiveness (lowest pregnancy rate) would be if they use an FABM correctly and consistently to avoid pregnancy. In this simulation study, we compare two different measures: (1) the method-related pregnancy rate; and (2) the correct use pregnancy rate. We show that the method-related pregnancy rate is biased too low if some users in the study are not using the method consistently to avoid pregnancy, while the correct use pregnancy rate obtains an accurate estimate. In FABM studies, the method-related pregnancy rate is biased too low, but the correct use pregnancy rate is unbiased.