The WNBA superstar shared the awesome news on her social media page ... gushing over Anya on their wedding anniversary while calling the pregnancy "surreal."

"I LOVE YOU🐞," Parker said in a message to Petrakova. "I appreciate you, I value you and what we have."

"We've always dreamed of growing our family...," Parker continued. "It's surreal that we now have a baby on the way!"

Of course, Parker has been a mother for 12 years -- she and Shelden Williams had their daughter, Lailaa, together back in May 2009.

And, Parker says Lailaa is fired up to welcome the new addition to the family, saying, "Lailaa is pumped to be a big sister!"

Parker added that she's grateful Petrakova has loved "Lailaa as your own" since the two got together.

"You couldn't be more beautiful!" Parker continued in her message to Petrakova. "Glowing, while understanding that I have to constantly love, kiss, and talk to your belly AND yes… play Jay-Z for the baby (Goose knows "Song Cry" already by heart😜!)"

"I can't wait to embark on this next chapter in life with you!"