After recently announcing her engagement to Alexis Ohanian, Reddit's co-founder, Williams announced the news of her "20 weeks" pregnancy on Snapchat, posting a photograph of her and her baby bump in a yellow swimsuit.
For Williams, who commands almost $29 million in salary and sponsorship earnings, becoming pregnant makes her all the more attractive to corporate sponsors, industry executives said.
Former world number one Victoria Azarenka of Belarus, 27, won the Indian Wells and Miami titles in March of previous year before missing the rest of the season as she awaited the birth of her first child in December.
Williams claimed her first Slam - the US Open - 18 years ago.
She hasn't played since, with a knee injury being blamed.
With a baby on the way Serena is not expected to play in any more competitions this year, however many outlets are reporting that she is likely to return to tennis in 2018.
Serena Williams has announced that she is pregnant, and while that is a wonderful development for her it will also have seismic impact on women's tennis.
James Pivarnik, a kinesiology professor at Michigan State University, said Williams' muscular build could forestall some of the changes that could impair performance. One fan wrote, "That means Serena Williams was pregnant when she won the Australian Open".More news: White House Misled Public About Defensive Measures Against North Korea
"It's not like some little 95 pound distance runner".
The tennis legend took to Snapchat today to share a photo of her showing her tummy, titled "20 weeks".
In pregnancy, a woman's center of gravity shifts forward to accommodate the growing fetus, which could affect Williams' stance.
Like Serena Williams said: "You just have to prove to yourself that you can go out there and be the best that you can be and not prove anything to anyone". This includes three Grand Slams - the French Open, Wimbledon and US Open.
"She'd be 30 weeks".
In the space of two years, Konta has gone from world number 151 to breaking the top 10, with her sights already set on the very top.
Her absence would leave the chase for the biggest prizes wide open for the likes of Britain's Jo Konta, now the world number seven. "It's not good for women's tennis which is a shame", she said. "You're part of that same age group, and once you've gotten over that mental hump of competing at this higher level in your 30s, which she obviously has, it is certainly possible".