Serena Williams was "terrified" when she discovered she needed an emergency Caesarean-section in order to deliver her baby. (HBO via AP)

Serena Williams was "terrified" when she discovered she needed an emergency Caesarean-section in order to deliver her baby.

The 36-year-old tennis star welcomed her daughter Alexis Olympia - whom she has with her husband Alexis Ohanian - in September last year and underwent the emergency procedure after suffering from chest pains 14 hours after her due date.

Serena opened up about the ordeal a few months after Olympia's birth, but in the season premiere of her new HBO documentary series 'Being Serena', she admitted feeling "a whole new kind of fear" when she was sent for surgery.

She said: "One minute, everything's going according to plan, and then I'm being wheeled off for surgery. I was terrified, and it was a whole new kind of fear."

Her husband, Reddit co-founder Alexis, added: "The C-section was low on our wish list because of her history with blood clots. Any surgery that Serena has is potentially life-threatening. But we decided, 'Well, OK, for the safety of Mom, for the safety of the baby, we have to proceed with a C-section." 

Serena had previously been feeling "pressure" whilst she was still pregnant with Olympia, as she revealed in the documentary that she became "anxious" with questions about how to become "the best" mother.

She said: "Becoming a mom, I definitely feel the pressure, and I feel a little anxiety. Am I going to be a good mom, a strict mom, not strict enough? I don't really know, so that anxiety has turned into nervousness and fear, and I'm really hesitant. It's the same attitude I have in tennis. I want to make sure I'm the best and I'm good enough."

The sporting star noted that she "almost died" from complications with Olympia's birth, but the process has pushed her to keep aiming for the top in both her life as a mother and her career on the court.

In the documentary, she added: "For so many years, I defined myself in just one way: by success, by championships, by making history. And then, all of the sudden, my life changed forever. It wasn't part of any plan to have this happen, not while I was still on top. But two years ago, I met this man, almost out of nowhere. We fell in love, and then, this unthinkable surprise. I can't believe how much went wrong on my way to meeting her. I almost died.

"But now, she's the reason why this all means even more than it did before. Still, there's no escaping the fear. The fear that I might not come back as strong as I was. The fear that I can't be both the best mother and the best tennis player in the world. I guess my only choice is to live and find out."

Bang Showbiz