The star announced her pregnancy in the video for her latest song, Never Worn White, revealing a baby bump in the final frames of the four-minute clip.
"OMG, so glad I don't have to suck it in anymore," she tweeted after the reveal, "or carry around a big purse".
Perry, who was previously married to Russell Brand, has been dating Bloom since 2016.
In an Instagram story, Perry told fans the couple were "excited" and "happy", and that the child was due around the same time as her sixth album.
"There's a lot that will be happening this summer," she said. "Not only will I be giving birth, literally, but also figuratively to something you guys have been waiting for.
"So let's just call it a double whammy. It's a two-for."
Perry explained the decision to reveal her pregnancy in a music video, saying: "I like to tell you guys everything but I knew I would tell you in the best way, which is through a piece of music because that's... I guess that's how I speak to you. That's how we speak together to each other."
She added that she'd started to develop food cravings. She now carries Tabasco sauce with her at all times and has been eating "the same burrito for weeks on end".