From studying the shape of their bump to deciphering different cravings, there are plenty of ways to guess the gender of a pregnant woman’s unborn baby. But Holly Willoughby has her own theory.

Testing it out on Serena Williams’ latest pregnancy photo, Holly revealed on ‘This Morning’ the way she normally predicts if a baby is a girl or boy.

Serena had shared an image of her bare bump on the cover of Vanity Fair magazine and asked fans if they could guess the sex of her baby.

Holly was quick to reveal she thought the tennis star was expecting a girl before going on to explain her ‘theory’ to This Morning viewers.

According to the mum-of-three, the key to finding out whether an unborn baby is male or female is to look at the mother’s hands when she rests them on the side of her bump.

“You see the shape of your hand if it goes in like that it’s a boy,” she explained as holding her hands on each side of her stomach to demonstrate.

“So if it goes in at the bump it’s a boy and if it goes out there then it’s a girl.”

“As I’m looking at the picture, she looks like she’s going out there,” the TV presenter continued.

“It’s hard to tell in a photo but if you’re pregnant at home do it, I tell you, it’s always right, it’s that shape.”

Holly’s gender prediction theory was revealed as the TV presenter has been on the receiving end of thin-shaming.

After photos of her wearing a floral gown at the Glamour awards emerged, Holly started getting some negative comments about her alleged weight loss.

People have also begun writing on her Instagram photos, saying that she looks “too skinny” or claiming they’re “worried” about her being too small.

“Holly lost too much weight. It makes her look older,” one commenter wrote on a photo of Holly in some short shorts.

Another said: “She’s getting too skinny- where’s [sic] the curves?!”

Others, however, have jumped to Holly’s defence, calling for an end to the body-shaming.

“It’s just as rude to say ‘you’re to thin’ as it is to say ‘you’re to fat’ I bet you wouldn’t say the fat comment to someone’s face,” one person pointed out.