Serena Williams on the harsh reality of 'cankles'

It's no secret that Serena Williams has very quickly become our favourite mama-to-be. From that accidental pregnancy announcement on Snapchat, to crowd-sourcing ideas for what to pack in her hospital bag, Williams has shared the ins and outs of her pregnancy journey with honesty and humour.

But while she recently highlighted an unexpected "perk" of expecting (hello Angelina Jolie lips), this week, Williams has discovered one of the not-so-glamourous side-effects of pregnancy.

"It's official," Williams tweeted to her nine million followers on Monday. "I no longer have ankles."

And her followers responded with a resounding: "Welcome to the cankle club!"

Along with those who'd been there and done that, other tweeters began sharing their own stories of the weird and wonderful changes that happen to the body during pregnancy.

Others said the swelling was definitely a clue to the sex of the baby:

In an interview with Vogue this week, Williams admitted that she's feeling nervous about childbirth - and that she's all for pain-relief.

"I'm not a spring chicken," she said. "The one thing I really want is an epidural, which I know a lot of people are against, but I've had surgeries galore, and I don't need to experience any more pain if I can avoid it."

The 35-year-old, who is engaged to Reddit co-founder Alexis Ohanian, also shared that she's not sure she's a "baby person" just yet.

"That's something I have to work on," Williams said. "I'm so used to me-me-me, taking care of my health, my body, my career. I always ask, Am I going to be good enough?"

And while the couple are waiting to find out the sex of their baby, Williams has a hunch she's expecting a baby girl.

"Two weeks after we found out [about the pregnancy] I played the Australian Open," Williams said. 

"I told Alexis it has to be a girl because there I was playing in 100-degree weather, and that baby never gave me any trouble. Ride or die. Women are tough that way."