She simply captioned the shot, shared on Tuesday 11 April: “Family of four 😍😍😍😍😍.”
The couple are yet to reveal the baby’s sex or name.
Myler also shared the same picture on his Instagram account with the caption: “Blessed 🙌🏻🙌🏻🙌🏻 #3becomes4.”
The couple announced they were expecting their second child together in November 2016.
Skelton shared a photo of her son Ernie holding a blackboard that read: “Ready for my partner in crime, due spring 2017.”
Skelton married Myler, an English professional rugby league footballer, in 2013. They welcomed their first child in June 2015.
In February 2016, Skelton opened up about the struggles of juggling work and motherhood.
“Ernie has turned my life upside down - in the best possible way,” she told the Daily Mail at the time.
“He needs me 24 hours a day, seven days a week and I’m pretty much the only person who can look after him - so I love being a mum, but it is full on.”