Serena Williams revealed pregnancy by accident after uploading '20 weeks' image to Snapchat

Serena Williams says she had no intention of making news of her pregnancy public after accidently uploading the “20 weeks” photo to Snapchat last week.

The 35-year-old is expecting her first child with fiancé, and Reddit co-founder, Alexis Ohanian.

But speaking at the TED conference in Vancouver, Williams admitted that the photo – which showed off her baby bump in a yellow swimming costume - was only intended for her own personal records.

"I have this thing where I've been checking my status and taking pictures every week to see how far along I'm getting," said Williams.

"I was just saving them (for myself). I've been so good about it, but this was the one time it slipped."

Williams also revealed that she only learned of her pregnancy two days before the start of the Australian Open – what would become her 23rd grand slam title.

"It wasn't very easy,” she added. “You hear all these stories about people when they're pregnant: they get sick, they get really tired, really stressed out," she said.

"I had to really take all that energy and put it in a paper bag, so to say, and throw it away.

"Pregnant or not, no one knew and I was supposed to win that tournament. Every time I play, I'm expected to win. If I don't win, it's actually much bigger news."

Quizzed over whether she would return to court, Williams said she hoped to see her child supporting her from the stands.

"I definitely plan on coming back. I'm not done yet," said Williams. "If she's [Venus, her 36-year-old sister] still playing, I know I can play.

"This (motherhood) is just a new part of my life. My baby's going to be in the stands and hopefully cheering for me."