Robert Griffin III -- My Wife Is Pregnant ... And My Marriage Is Solid!!

There could be an RG4 in Robert Griffin's future -- because the NFL star just announced his wife is pregnant with their very first child!!

Griffin -- who's celebrating his 25th bday today -- made the announcement on Twitter ... posting one of those baby announcement photos along with a caption that reads:

"BIG thank you for making this birthday a special day!!! This year's gift will change our life forever!!! #BoyOrGirl"

The photo is interesting though ... considering his wife Rebecca seemed to make a point to include a shot of her ring finger with her big honkin' diamond on it.

It almost seems like she's making a statement about the state of her marriage ... after reports a while back suggested things may have been rocky at home.

Or maybe she just wanted to remind everyone she's got a baller diamond.

Either way ... congrats!!