The 22-year-old is eight months pregnant with fiancé Thomas Cohen's son and her due date is April 24 - the birthday of her late mother Paula Yates.
After telling a follower that she had "a tummy like a hot air balloon", Geldof uploaded a picture of her stomach complete with the caption: "Can now officially not see my feet! He's getting big in there."
She added later: "I've seen the most clear pics of him in the 4D ultrasound's he is SO cute! He looks like a mini hybrid of me and Tom."
Speaking about her pregnancy in January, the presenter and model revealed that her father Sir Bob Geldof was delighted to discover that she was having a boy.
"Oh my God, he was so happy... The poor man's been surrounded by women up till now," she said. "I knew he would be happy but I didn't realise how over the moon he would be.
"He's always been very supportive of me but he was really overwhelmed and emotional."