"I find it disturbing that society loves to critique a woman's shape no matter how beautiful or happy she may be within herself," began Khloé. "I am a first hand victim to public attacking in regards to my body or appearance. That is low in and of itself. But I can not tolerate one more vicious attack on my sister!"
"For anyone to ever criticize a woman who is growing another life inside of her is true scum," she added. "Stop being so careless with your words... words are a powerful weapon, all I ask is that you think about the consequences of your words... choose them wisely."
Khloé, 28, who runs clothing line D-A-S-H her sisters Kim, 32, and Kourtney, 34, then addressed her sister directly.
"Kim, you may be one of strongest people I know," wrote Khloé. "I have no idea how you endure such abuse but still smile and shine everyday."
"I commend you for not putting your head down and going into hiding like so many would," she continued. "You live your life and you try to make the best out of a tough situation. I need you to know how truly magnificent you are!"
Khloé's timely words of kindness touched Kim, who tweeted her appreciation to her younger sister.
"I love you very much @KhloeKardashian!" said Kim. "Thank you so much for this amazing note!"
Khloé's letter closely follows Cheryl Cole's supportive tweet to Kim, who is fast approaching her July due date.
Kim sent a message of thanks to Cheryl, 29, reached out to Kim on Twitter, calling her an "incredibly beautiful woman" and saying she saying she admired her tenacity.
"Dear @kimkardashian. Hi Gorgeous lady! Just wanted to send you a tweet to say I think you are an incredibly beautiful woman inside and out," she wrote.
Kim, who is expecting her first child with rapper boyfriend Kanye West, 35, has received a lot of criticism since falling pregnant, with particular focus on her maternity wear choices. She recently revealed she has completely lost her body confidence and now resorts to wearing "anything that fits".
The couple have been having a tough time recently, with media intrusion at an all-time high — Kim narrowly avoided a car crash with a zealous member of the paparazzi last week.