Berlin - It was an impressive sporting feat when Serena Williams won the record No. 23 Grand Slam singles title at the 2017 Australian Open, beating her sister Venus in the final. Not long after, a revelation: she was pregnant at that time.

"Honestly, I don't know how I did it," Williams said at an event on Wednesday, choosing the most important moments of her tennis career.

After winning her first Grand Slam at the U.S. Open in 1999, Williams went on to be the only player to win the "Golden Grand Slam" - winning the Australian Open, the French Open, Wimbledon and the U.S. Open and winning the Olympic gold medal.

"I don't know what I'm doing, I've been pregnant for nine weeks...I do remember not being able to run for a long time," Williams said at a Superturn private equity meeting in Berlin.

"I didn't tell anyone. I mean, Venus knew, I still felt very sad about it because part of me felt like it was because we played each other in the finals, I must have known that she must have known it, and she must have felt a bit deep heavy, even going further and going all out. But she was just one of two people who knew it."

Early pregnancy symptoms can be strong because of a huge change in the body, and a surge in hormones can often lead to fatigue, dyspnea and nausea.

"I remember saying, I had to do a lot of aces, I had to do a lot of winners," Williams continued. "I can only play four balls, I'm done."

“I remember one time playing a player that was so long that I couldn’t breathe.

Williams, who has two daughters with investor and Reddit co-founder Alexis Ohanian, who quit professional tennis in 2022 to focus on her family.

Sports stars such as Laura Kenny, who have spoken in recent years about the challenge of balancing a strong and physically demanding career with a desire to get pregnant, while tennis player Naomi Osaka criticized public comments that one must be sacrificed for another.

Williams now runs Serena Ventures, a venture capital fund with 40 portfolio companies.

She told private equity professionals that crowded listeners have made her obsessed with the quality she won in sports competitions translate into a one-on-one focus of investors.

“I do remember one time walking on Wimbledon’s court, when my partner called me about the deal we were trying to complete,” she recalled.

"I was in court that day and walked a long way. I remember talking to her on the phone, and in the conversation, she was like... How is your day? I'm in court now. She was like: She was like: You're kidding me, you have to get off the phone. You like, okay, okay, my intention.

She points out that she looks for founders who are obsessed with what they do and change the lives of those they want to influence.

Her earliest investment was in the 2009 US soccer team Miami Dolphins, when she was the highest-ranked female player in the world.

"About why we shouldn't do that. We just need to focus on tennis, we don't need to think about that," she said of the media and sports reactions at the time.

"Now, as athletes, we're at the point where you're just playing basketball or just playing football, if you're just playing tennis, it's like, what are you doing? You're also giving people a platform to make people like this, that's OK. You can be an entrepreneur, and you can do sports. You don't have to stay in a lane, you know, you know, you know, you can do one."