Serena Williams and fiancé Alexis Ohanian are waiting to find out the sex of their baby, they told reporters at the Met Gala.

Serena Williams stepped out in style at the Met Gala in New York – and revealed that she does not yet know whether her new baby will be a boy or a girl.

With fiancé Alexis Ohanian by her side, she told Vogue reporter André Leon Talley that they have chosen not to find out the baby’s sex.

“We are waiting!” said the Australian Open champion. “We will wait for a surprise. We call it ‘baby’.”

Ohanian paid tribute to his fiancée on the Humans of New York website, saying: "She has the biggest heart. Everyone sees her success as an athlete, but all of that is layered on the size of her heart. She gives 100 per cent of herself to everything she does: as a friend, as a lover, and soon, as a mother."

Williams confirmed her pregnancy last month – having accidentally announced it via a rogue photo on Snapchat.

She will be taking the rest of 2017 as maternity leave but plans to return to competition next year.