Everything around Steve seemed to turn to a blur for some reason. It kinda felt like being in a sensory deprivation tank with how the outside world didn't seem to exist anymore. All of a sudden, he saw something on the screen that was rendered with far more sophisticated visuals than he'd expected- someone's conception. A whole bunch of sperm swimming towards an ovum, all desperate to fertilize it. Soon they reached it, and one buried inside, but he realised one of the sperm that had not gotten inside felt... familiar. A moment later, he realised that sperm was him!
A sort of timelapse followed, with the fertilised egg implanting itself in the womb and starting to develop. After a little while, Steve felt something odd watching it- like it had missed a step. That was when it dawned on him that the sperm must have had an X chromosome. He remembered from biology lessons that at a certain point in foetal development, the body diverges depending on the sex chromosome of the sperm. In other words, it was developing into a girl instead of a boy.
Now Steve's body became illuminated, and he looked down to realise his clothes had vanished. As the foetus continued to develop, his changed too- he saw his penis shrink away to nothing, felt his balls recede inside the body and turn into ovaries, she shrank several inches, her body's proportions altered to be more petite and curvaceous, her skin softened and smoothed, and large soft breasts swelled up on her chest while between her legs a vaginal slit formed. At this point she noticed she had mentally adopted to the idea of being a girl.
Steve- or rather, she realised, Stevie- now noticed the foetus she had developed from was now almost ready to be born. And as it was, everything went bright white, and she found herself in a woman's bedroom. Her bedroom.
And when she looked in her wardrobe, she realised what she did as a girl. She was...