WNBA's Brittney Griner -- My Wife Is Preggo!

WNBA superstar Brittney Griner is going to be a mom ... 'cause her WNBA wife Glory Johnson has announced she's got a bun in the oven.

The couple is obviously moving quickly -- they were just married last month.

Sources close to the couple tell us they found out just a few weeks ago -- and insist Johnson was NOT pregnant at the time of the domestic violence incident in Arizona back in April.

Clearly, the couple used a sperm donor ... though the donor's identity has not been revealed at this point.

24-year-old Johnson made the announcement on her Instagram page -- showing a picture of a bun in an oven ... with the caption, "#WelcomeToTheJohnsonGrinerFamily."

The WNBA season is set to begin Friday -- we're told Glory will NOT play this season.

No word on how this will impact her 7 game suspension stemming from her domestic violence arrest back in April.

Sources close to the couple tell us Griner and Johnson had been planning to have a family through artificial insemination for months ... and they began trying right around the time of the wedding.

Congrats!