Is this word a relatively recent invention or has it slipped past my radar for most of my life?
Craigers got Meggers preggers at the keggers. :eek:
I saw it for the first time in the “National Enquirer” about Melanie Griffith, but I don’t recall whether she was carrying Don Johnson’s or Antonio Banderas’s child. However, I did hear the term “preggie” on “All in the Family back in the 1970s.
The OED dates it from 1942. However, I think it was primarily a British term for most of the time since then.
“Preggy” is from 1938, and “Preggo” is from 1951. I think that “preggo” was the American slang until “preggers” took over.
According to Etymology Online, “preggers” dates to 1942. At a guess, I would expect it to be an English term, since they had a tendency to make such words, including “ruggers” for Rugby football, and “soccer” from Assoc. football. samclem can provide actual details, I am sure. 
I don’t have a cite, but - to echo DSYoungEsq - my understanding is that the -ggers suffix was once a common habit in English school/undergraduate slang.
Hence “Staggers” (for example, in this article) as the traditional nickname for the New Statesman magazine.
Fo’ shizzle, my nizzle. 
Taken to extreme, upper-class lengths, a Waste Paper Basket is a wagger pagger bagger. Bloody toffs.
While the evidence seems to point towards Britain, I would blame the Aussies. They seem to have inherited some gene that makes them incapable of using whole words or names.
Preggie may have some ancient British usage but it is in full modern use in Aussie (Australia), NZer’s as close cousins, use preggers in very familar and informal settings.
Bloody Aussies will shorten anything if it stands still long enough!
No, wagger pagger is ‘War And Peace’.
That’s as may be. But W - aste P - aper B - in is a W- agger P - agger B -agger.
OK, now do “bun in the oven.”
Must be that time of the month…
Lots more on the origin of preggers in this thread (e.g. Rod Hill’s post).