"How are you sooooo tiny!!!!!! I was huge at 6 months," one woman asked.
"She's 6 months prego! How?!" another said.
"Where tf the bump at," a third commented.
While many appeared baffled by Bella's baby bump, some quickly came to her defence.
"Interesting how our bodies are different. At 6 months I was huuuge. You look elegantly pregnant," one woman said.
"@belle_lucia you are bossing pregnancy, and glowing over the negativity! I wished I would have looked like this when I was pregnant, but the end result is the same," added another.
"Her bod is better than mine and she's pregnant. What an absolute babe," someone else remarked.
In a post she shared last Monday, the mother-to-be who is half German and half Portuguese said since becoming pregnant all she wanted to do was swim.
"Just slightly difficult living in London as I can't quickly jump into the ocean like I did back in Australia," she added, alongside a post of entering what appears to be a hot tub at the St Pancras Renaissance Hotel in London.
The post also racked up hundreds of comments, with fans in disbelief the model is six months pregnant.
People questioned how she could still be rocking a toned stomach this far gone, while others continued to claim she looked better pregnant than they did on an average day.
"She's 6 months pregnant and I look more pregnant and I'm not even pregnant," one woman said.
"How is this a 6 months pregnant stomach if only everyone was like that."
A third asked: "Are you pregnant in this photo?"
Someone else questioned: "I'm so confused are you actually pregnant?"
It's not the first time Belle's bump has been questioned, as the model claims she was forced to delete her ultrasound post as people were being "creepy and rude".
Her baby bump was branded "tiny", but Belle hit out at her haters.
Posting on her Instagram story, she wrote: "As you can see, women show very differently but are all carrying a little life.
"Just because I'm not showing as much as you like doesn't mean my pregnancy is 'unhealthy' or that I'm promoting a 'skinny' pregnancy.
"It's just my body and I can't help it if it doesn't look the same as other women.
"Body shaming is not okay no matter how 'big' or 'small' someone is."
And she also shared the "side she never shows" after uploading a video of herself experiencing morning sickness.
"Just so you know pregnancy isn't all daisies and roses, currently locked in a train bathroom violently throwing up."
Sharing her pregnancy journey with her fans, Belle wrote: "I did experience morning sickness, breast pain and definitely a lot of anxiety on the beginning because of the fear of miscarriage - I had no idea how common they were.
"But I've learned to embrace everything — both the downs and the ups."
