Influence of cycle variability and coital frequency on the risk of pregnancy

Researchers have cautioned against generalizing results from contraceptive trials because these studies rely on self-selected participants meeting str ict selection criteria who may differ from typical users. Using information collected on daily diaries, we reanalyzed data from the recently completed Reality(R) female condom clinical trial to evaluate factors that influence the probability of pregnancy. Noncompliant women, women with less variable menstrual cycles (17-43 days), and women engaging in intercourse frequentl y (greater than or equal to 11 acts per month) were more likely: to conceiv e during this 8-month trial. The adjusted hazard ratios and 95% confidence intervals for these three covariates were 6.1 (2.0-18.7), 7.2 (1.0-54.3), a nd 2.0 (0.7-5.3), respectively The strict selection criteria used in this s tudy failed to recruit a homogeneous cohort with respect to factors that in fluence the risk of pregnancy. The overall pregnancy rate does not pertain to individual study participants, but rather represent average effects for a population with the particular mix of characteristics found in this study . In particular, we not only confirm the well known importance of complianc e and the obvious role of frequency of intercourse, but also demonstrate th at women with cycles outside the range of 17-43 days appear to be at a much lower risk of pregnancy.