Serena Williams and fiance Alexis Ohanian welcome baby girl

Serena Williams has given birth to a baby girl. The tennis champion welcomed her first child with her fiancé, Reddit cofounder Alexis Ohanian at a hospital in Palm Beach, Florida,on Friday (1 September).

A source close to the tennis pro told Us Weekly the baby was induced and weighed 6 pounds 13 ounces. Mother and baby are both doing well.

Williams accidentally announced her pregnancy in a Snapchat photo on April 19 posting a selfie that showed off her tiny baby bump. She added a caption "20 weeks" pregnant, but had not released the post was public.

According to reports, the 35-year-old sports star checked into the hospital on Wednesday, with an entire floor of the location being closed to any unauthorised personnel to ensure her privacy.

While the couple had chosen to keep the sex of their child a secret until her birth, the 23-time Grand Slam winner said was convinced she was having a girl.

"Two weeks after we found out [I was pregnant], I played the Australian Open," she recalled.

"I told Alexis it has to be a girl because there I was playing in 100-degree weather, and that baby never gave me any trouble. Ride or die. Women are tough that way."

Singer Beyonce was the first of Serena's celebrity friends to congraulate her on social media. The Halo star shared a photo of the tennis player in a flowing white dress, taken from William's photo shoot for the September issue of Vogue. She added the message: "Congratulations Serena!"

Anticipating the birth of her baby, earlier this week Williams shared a video on Snapchat which she titled 'How athletes look at pregnancy' as she drew a diagram on her belly,

"So baby's head is here," she explained pointing to her lower abdomen. "Good job, you want it to stay there," she added. "You have the feet maybe over here or a little bit over here,' she added as she moved the pen to her right side.

"The hands - I kind feel it punching - are over here' as she drew a circle in the lower right quadrant of her tummy."

Ever the sports pro with her eye on the ball, she instructed her unborn child: "Be focused when you come out."

Earlier Williams revealed her plans to compete in next year's Australian Open – just four months after giving birth. "It's the most outrageous plan," she told Vogue. "I just want to put that out there. That's, like, three months after I give birth. I'm not walking anything back, but I'm just saying it's pretty intense.

She added: "In this game you can go dark fast. If I lose, and I lose again, it's like, she's done. Especially since I'm not 20 years old. I'll tell you this much: I won't win less. Either I win, or I don't play."