Do you really believe it was that and not simply more of Roddenberry's teenage male approach to sex through which he tried to shoehorn as much cheap romance novel crap into Trek as he could? I suspect the latter.
Why on Earth couldn't it have been both
I would not have had that useless and unused bio-monitor on the belly either.
Just because the perscan technology wasn't described in dialog doesn't mean that the devices were "useless and unused" considering that they were directly inspired by NASA's biobelt instrumentation
developed for the Apollo Program. When one takes into account that starship crewmembers are routinely exposed to alien biospheres on a more or less weekly basis while on a 5YM the necessity of just such an uninterrupted biotelemetry system should become self-evident.