Serena Williams' 2017 Met Gala ensemble was a ''defining moment'' for her, according to stylist Kesha McLeod.

The 35-year-old professional tennis player is expecting her first child with her fiancé Alexis Ohanian, and showing off her burgeoning baby bump in the emerald green Atelier Versace floor-length gown to the star-studded bash earlier this month has been described as the ''avant-garde element'' for the sportswoman.

Speaking about the brunette beauty and her wardrobe choices for the red carpet bash, the style guru told Refinery29: ''It was a super-complicated, beautiful gown with a long train.

''Since it was such an avant-garde theme this year, Serena's belly basically was the avant-garde element; it was a defining fashion moment for Serena.

''Women usually throw on big, oversized dresses or the caftan. As Serena's Met Gala dress showed, you can still wear a full-on gown, with a long train.''

Serena also took to social media at the time to show off her elegant gown, and reveal the details of where her full outfit was from, including the accessories.

Alongside a picture of her and her beau at the event, which was shared on her Instagram account, read: ''Watch: the Diamond outrage by one of my partners @audemarspiguet Dress @donatella_versace @versace_official earrings: @xivkarats overall: LOVE (sic).''

And the athlete - who took home the trophy at the 2016 Wimbledon Championship for both women's singles, and women's doubles where her partner was 36-year-old sister Venus - has been praised for having a good fashion sense.

Kesha - who has worked with Serena for seven years - continued: ''[Serena is] really into fashion and she gets it.''

Meanwhile, the fashion expert has hinted Serena has yet to slip into maternity garments, although she thinks it won't be long until she requires the specialised items.

She said: ''Give it some time.

''By the seven- or eight-month-mark, everyone is like 'Give me a maternity dress.'''