Question is self-explanatory. Just curious and want to expand my knowledge of English.
A pregnant pause is a pause that builds up suspension in the listener/viewer, for a greater dramatic (especially comic) effect of what follows after the pause.
Edit: Merriam-Webster has this:
3. rich in significance or implication <the pregnant phrases of the Bible — Edmund Wilson> <a pregnant pause>
Wikipedia has this bit specifically on comic timing:
A pregnant pause (as in the classical definition, "many possibilities") is a technique of comic timing used to accentuate a comedy element, where the comic pauses at the end of a phrase to build up suspense. It's often used at the end of a comically awkward statement or in the silence after a seemingly non-comic phrase to build up a comeback. Refined by Jack Benny, the pregnant pause has become a staple of stand-up comedy.
I've always taken it to mean a pause that engenders an expectation ("pregnant" = "expecting") for the listener. This as opposed to a pause to let the listener reflect on what was just said, a pause for the speaker to catch his breath, a pause for the speaker to find the right words, etc.
It could be used in telling a joke, making a sales pitch, storytelling, or as a form of emphasis that can only be described as legen...
(wait for it)
A pregnant pause is one that takes on the characteristic of being anticipatory, but inscrutable, to the observer, whether by design or not, of the pause maker. In the sense that pregnancy is an anticipated but uncertain revelation in the making, a pregnant pause is an anticipated but uncertain utterance in the making.
I have a slightly different use case, although it ties in with what has already been stated. When I say, 'I... when my mother... died, I', I am trying to indicate to the listeners that there is something that I am not saying and that if they want to know about it, they are going to have to draw that information out of me.