The British Board of Film Classification (BBFC) has revealed that in order to reach the new rating, seven seconds of footage has either been cut or replaced.
Lions Gate UK Ltd edited a particular scene by removing images of "blood splashes".
"The company chose to make cuts in order to achieve a '12A' classification," the report states. "A number of cuts were made in one scene to reduce an emphasis on blood and injury.
"These cuts, which were implemented by digitally removing sight of blood splashes and sight of blood on wounds and weapons, were made in accordance with BBFC Guidelines and policy. An uncut '15' classification was available.
"These cuts were made in addition to reductions already made following an earlier 'advice' viewing of an incomplete version."
The Hunger Games is based on the popular trilogy of books from Suzanne Collins, and is said to be out-selling Twilight sequel Eclipse in box office pre-sales in the US.
Jennifer Lawrence, Lenny Kravitz, Liam Hemsworth, Elizabeth Banks and Donald Sutherland star in The Hunger Games, which opens in cinemas on March 23.
It will be premiered in the US tonight (March 12), with the UK premiere taking place at The O2 on Wednesday (March 14).
> The Hunger Games video: Peeta Mellark's pre-games interview
Watch the trailer for The Hunger Games below: