Not necessarily decreasing them at the same time, no.
I wanted to research the question what the (virgins devirgined):(new virgins created) during standard sexual intercourse would be.
I looked and found
this study. It did not answer my questions, but raised a few eyebrows. The whole dataset can be downloaded
here. I used
this PDF.
Among other things, people were asked to imagine their perfect relationship, given a deck with cards with events such as "we would kiss", "we would get married" etc and throw out the ones that don't imagine happening in their perfect relationship (page 460 and following of the PDF). Afterwards, sort the cards they kept by "what would the first/second/... stage of said perfect relationship be".
Apparently, 13 out of 6345 of the participants consider "my partner or I would get pregnant" the ideal first step in a relationship
Interestingly, that's one more than the "ideal first step would be sex" group.
In other news, 466 out of 6380 participants do not consider "we would kiss" to be part of their perfect relationship. 3533 out of 6380 would not have sex.