Stanford & Dunson. (2007) Effects of sexual intercourse patterns in time to pregnancy studies. Am J Epid 165(9).
Key Results
“Our analysis shows that variations in the timing, as well as the frequency, of intercourse may affect TTP. Our simulations indicate that there is a potential for confounding of results of TTP studies if sexual behavior relative to the fecund window is not carefully considered in the analysis. As expected, the model demonstrates in figures 1 and 2 that increasing the mean frequency of intercourse decreases the mean time to pregnancy in a nonlinear fashion, with the decreasing marginal effects on reducing TTP at higher mean frequencies of intercourse. However, it is also clear that, even with a constant overall frequency of intercourse in the fecund window, there can be substantial effects of the timing of intercourse.”
Conclusion
“Having demonstrated differences in TTP based on intercourse patterns that include both frequency and timing of intercourse, we conclude that it is valuable to obtain data that will facilitate an analysis of day-specific probabilities of conception, to the extent possible within a specific study.”