[Danny Stewart]

"Something Borrowed" by Phil Ford
Gwen is late for her hen night, as she was called in by Torchwood to chase down a shape-shifting alien. She follows it, eventually engaging him in a fight wherein he bites her arm before he is killed by Jack. The next morning they discover that the alien had transferred fertilised eggs into Gwen, which have matured inside her body to the point where she now appears pregnant.