Why you..?

you were one of the only male science experiments in the facility, so why not put your body too use...literally. The scientists wanted to know if it was possible to put an artificial uterus inside of a man's stomach and bare children. So what do they do? They take you, and use you as a test. But they won't try to grow an actual fetus in the your stomach, no; that's too risky for a trial and error test..

you wake up from the surgery back in your enclosure, your mind still hazy from the drugs they used to put you under. You slowly sit up, your stomach slightly sore from the implant. You look down, seeing the stitches...but it feels hard to the touch. A scientist comes in the room and smiles.

Scientist: "The implant was successful. You won't start seeing any changes until a few weeks from now when the worms start growing larger.."