The 33-year-old, who is already mum to one-year-old Ernie with her husband Richie Myler, posted the snap of her posing by the pool where she lives in France.
“Countdown...” she wrote on Thursday 16 March, alongside the hashtags #pregnancy, #bump and #37weeks.
Fans told the mum she was looking “fab” so far along in her pregnancy.
“I’m so jealous,” one mum wrote. “32 weeks here and I look like I’ve developed my own solar system. You’re looking so great.”
Another mum wrote: “Snap, you look amazing compared to me who feels like a whale.”
Skelton announced she was expecting her second child in December 2016.
She shared a photo of a chirpy-looking Ernie holding a blackboard that read: “Ready for my partner in crime, due spring 2017.”
Skelton has previously opened up about the struggles of having a toddler when her son had a tantrum at playgroup.
She shared what happened on Twitter and was “overwhelmed” with the messages of support she received.
“I had loads of women message me and say: ‘That exact thing happened to me’,” she told The Mirror in February. “That’s so nice as we’re all under pressure to be amazing mums.
“If my tweet made one stressed out mum somewhere say, ‘Thank God, it’s not just me’, then that’s amazing.”
Skelton married Myler, an English professional rugby league footballer, in 2013. Their first child was born in June 2015.