“I’m happy to confirm Serena is expecting a baby this Fall,” publicist Kelly Bush Novak said in an email to AFP.
No further details were immediately available.
Tennis superstar Williams sparked widespread speculation earlier on Wednesday that she is pregnant, posting a photo of herself in a yellow one-piece bathing suit on the social media site Snapchat with the caption “20 weeks”.
The 35-year-old, who will return to the No 1 ranking in the world next week, deleted the photo shortly after it appeared, and she had not commented further several hours later.
A representative for Williams declined to comment at the time on whether the post was a confirmation that she is pregnant.
Williams is 20 weeks into her term, which would mean she was approximately two months pregnant when she captured her record 23rd Grand Slam tournament title at the Australian Open in January.
Her victory over older sister Venus Williams broke a tie with Steffi Graf for the most Grand Slam singles titles in the sport’s modern era.
Serena Williams has not played since, citing a knee injury.
Fans and celebrities reacted with a mixture of awe and glee to Williams’ Snapchat post.
“Serena Williams was pregnant when she won her 23rd grand slam tournament at the Australian Open. And did not drop ONE SET. Let that sink in,” wrote Twitter user @noelleharmony.
The next Grand Slam tournament this year is the French Open, which starts in May. If Williams is 20 weeks pregnant and gives birth after a full term, she would have her child in early September, during the fourth Grand Slam, the US Open in New York.
Williams, the highest-paid female athlete in the world, announced her engagement to Reddit co-founder Alexis Ohanian last December.