Well, unfortunately it seems that Kurst was exposed to a little radiation, causing a very minor mutation...one that just happens to let his body bypass the birth control chemicals, as Valentine has discovered a few months later. Kurst is being looked at, but regardless of what happens to him, Valentine just has to keep up with her work duties despite a very snug vault suit.
Art by aggro_badger
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Zarpaulus
I don't recall reading an explicit statement that Kurst was the father back on FA. Though I suspected it.