Alongside the photo of her baby, which can be clearly seen, the excited reality TV star wrote, "I can't believe this is ours @kevinjonas and I are so blessed. Look at that cute nose !!!"
The 25-year-old and her husband Kevin shared the good news that they are going to be parents in July.
"It's true @daniellejonas is pregnant! can't even imagine how excited we are I can't wait to share this with my best friend. I love you baby," Kevin tweeted to his more than 3 million followers.
More recently the mum-to-be shared that the excitement of not knowing the sex of the baby was too much. She posted an adorable pic of yellow and white baby booties with little ducks on and said, "So excited just bought my first thing for baby !! Don't no what it is yet its killing me !"
It seems that for now the eldest member of the Jonas Brothers and his wife are keeping that news to themselves, perhaps inspired by Prince William and Kate Middleton, who didn’t know the sex of their baby until he was born.
Kevin, 25, wed former hairdresser Danielle during a fairytale ceremony at Oheka Castle, a French-style chateau on a sprawling estate in Long Island in 2009.
Just over 400 friends and family members attended the fairytale forest-themed event, which saw 14ft trees covered in hydrangeas and crystals designed to look like icicles.
The bride, who was 23 at the time, wore a Vera Wang gown along with a silk and crystal flower in her hair. This served as a reminder of the flower she wore in her hair the day the pair met in 2007 on the beach in the Bahamas.
Kevin and Danielle became the stars of their own reality series, Married to Jonas, in 2012. The E! show, produced by Ryan Seacrest Productions, which is also behind Keeping Up With The Kardashians, gave fans a behind-the-scenes insight into their young love.