I’ve always been curious–whenever you hear somebody talking about a particular type of female-stuff doctor, they refer to them as an O-B-G-Y-N (using each individual letter).
Since the full term is “obstetrician-gynecologist,” it seems to just roll trippingly off the tongue to call them “Ob-gynes” (pronouncing the words) but nobody does. Anybody have any idea why? Why use five syllables when it’s just as easy and understandable to use two?
I did say it was trivial. 
It’s just the venacular that becomes most common is the one that is used.
In my part of the country, we say “Oh Bee Gin’s” or just “Oh Bee’s” as the practice of Obstretrics and gynocology are two separate specialties, although somewhat related.
Not needing the OB part, I say gynie and people know what I’m talking about. Doesn’t answer your question, I know…
I work with physicians who focus on fertility and women’s health. It really varies, but folks in the biz refer to them as “OB’s” “obee-gynee’s” “O.B.G.Y.N’s” and “referring physicians” 
It’s certainly not a trivial question, but there is no official “inside baseball” answer that I am aware of…
Weird. I’ve never heard it pronounced, but had no clue it would be anything other than “Ob-guyn” (to rhyme with “wine”). “O-B-G-Y-N” is just silly.
Interesting. Maybe it’s just a regional thing (I’m in the SF Bay Area, California), and that’s the only way I ever hear it pronounced (they used it on the news last night, which is what got me to thinking about it again).
I’ve only ever heard O-B-G-Y-N or gynocologist. I always thought it was indecision over how to pronounce the g-y-n. As part of a word, it’s obviously guyn. On it’s own, my first urge is to pronounce it gin, but no, as a shortening it’s guyn, but it looks like gin . . .
This just resurrected a memory of some SNL lady singing a romantic song about her “Caribbean Gyno.”
Yeah. My wife just says “gyno.”
I’ve heard other women say “o-b-g-y-n” but never anything like ob-gyn.
O-b-g-y-n, or gyno. Never heard out pronounced as words. I’m In virginia.
O-B-Gyn
My father used to have some association with a magazine called “Contemporary Ob/Gyn” and he always pronounced it “OB-GYNE”. Workplace was in New Jersey near NYC.
Huh. My dad’s a doctor (family practice) and we’ve always pronounced it “O-B-gin.” So you say the O, you say the B, then you add a “gin” at the end (like the liquor). Never “gyne” (to rhyme with “wine.”)
Differences - it’s what makes the world go 'round!
I pronounce it like this as well. It’s a two syllable word.
I used to work medical records for an Ob/Gyn clinic. Everyone there used O-B-G-Y-N.
G-Y-N actually rolls off the tongue about as quickly and easily as ‘gin’ does, despite being three syllables, and it avoids the potential embarrassment of being called out for mispronouncing it.
A LONG time ago I used to work for the Obstretics and Gynecology department of a university research hospital. Everyone said “oh-bee guy-nee.” It seemed strange to me at first, but I got used to it.
I’m not saying it is pronounced as ob-guyn here, just that I’ve never heard it spoken out loud but if I had to read it then that’s how I would say it. (And, evidently, make an arse of myself.)