We apply an extension of a statistical model developed in the fertility research setting to the barrier contraceptive trial setting to obtain estimates of the probability of pregnancy per cycle day in the presence or absence of barrier use among participants of a randomised trial of female barrier contraceptives. The per cycle day pregnancy curve for the barrier trial participants was similar to previously published results from a fertility study that included a precise indicator of ovulation day. In addition, our analysis showed strong contraceptive effects for the diaphragm. The proposed modelling approach should allow evaluation of the effects of other coitus-specific exposures on the chance of pregnancy in other prospective studies, including fertility studies.