Your doc might request to do an internal at your 30wk (or close) to determine cervical health and chance of early labor.
No one looks down there for very long like a pap, they just lift the sheet, see where to put their fingers, insert as they drop the sheet back, do a quick check, then your done.

Took me longer to type this than it actually takes in real life.
I was supposed to have one at my last appt, doc said "Baby is still really high, so I don't think we need to check you today."
whew.
But I expect they'll start checking shortly.
As far as the infection thing goes, they use gloved hands and it takes all of 2.3 seconds (unless something is awry and then you have the benefit of knowing ahead of time if early labor might happen).
I would think having sex would introduce more infectious problems than docs gloved fingers. And that is completely natural and supported in pregnancy unless there are prelabor issues.
Anyway, it is your right to refuse, and not do anything you aren't completely comfortable with.
