Meg Ireland, 25, who runs The Shutupmeg Blog, pleaded at others to be "cautious" about what they're posting and who follows them online.
Posting a photo of her bump picture she found on another site, Ireland wrote: "This bump pic along with around 15 other pictures of mine ended up on an online 'preggophilia' site, which is a porn site for people who like pregnant women."
Ireland said while she believes women shouldn't have to worry about others "stealing" their photos, it's something they can't avoid.
"I see so many people upload their bump pics and now I just gasp and hope to God they don't get into the hands of someone they shouldn't," she wrote on the post.
"When I was scrolling through this God awful site trying to find where this thread was, I saw some pretty fucked up shit.
"People were uploading pictures of their wives to other users, brother-in-laws uploading pictures of their sister-in-laws and women uploading pictures of their work colleagues. I literally couldn't believe what I was seeing."
Ireland also addressed some of the comments she'd received after people argued she is to blame for posting the pictures in the first place.
"People would say I should only blame myself for uploading 'personal pictures' and that it was my own fault (even though my profile was then private)," she added.
"I see it differently. I didn't care that someone had screenshot my photo to show someone, it was what they did with my photo(s) that made me physically sick to my stomach.
"Why should we have to sit and worry about this when uploading a photo on our social media sites?
"Please be cautious about who follows/adds you. Block them if they look like a creepy MF."
Ireland believes the pictures were taken from a private mother's group she joined in 2014 when she was pregnant.
"One person in the group was a fake and was using my picture to encourage other ladies to post pictures of their bellies so they could steal them and post them on these bizarre sites," she claimed, speaking to Daily Mail Australia.
"I emailed the website after having to go through all the horrible content to try and find it... they took it down after I threatened legal action."
Ireland said she just wants to "spread awareness" and make sure others realise there are people out there targeting pregnant women online.