Ty soon noticed that the sensation running through him now felt different to how the fetus which he had been produced by had. It felt nice- maybe even nicer than what he was used to- but he felt confused why. He could guess, but decided to wish to know for sure.
And, sure enough, his wish informed him his sperm form had not had a Y chromosome, but an X. This time, Ty would be born female instead of male.
He saw the person he had been before he regressed himself to get re-conceived, and before his eyes his body was reshaped by the genes the man and woman who had conceived him had provided. At first it was fairly innocuous- his face altered to resemble them, his muscle mass and proportions seemed to shift a little- but soon his, or rather her, new gender began to assert itself.
His figure feminized, shoulders slinking inwards while hips expanded to child-bearing proportions. His skin softened and smoothed all over, most of his body hair receding or vanishing. All over, he seemed to shrink subtly- his neck, his arms and legs, his hands and feet, his height, it all seemed to draw inwards to proportions more befitting a young woman than a young man.
Just to make Ty realize questioning that was futile, the opposite gametes of her new form set about inverting his sex. An aching, empty sensation emerged in his lower body as he felt his penis start to recede into him, and his chest grew sensitive as his nipples swelled up. As his feminine mammaries grew, his masculine shaft shrank, and soon his testicles pulled up inside him to change into ovaries. Ty's grip on his masculinity was loosening- she was starting to adjust to womanhood. Soon her penis settled into its new hood and formed a clitoris, and her scrotum split into vaginal lips.
As Ty's perspective moved back to her fetal form, she realized she was a girl now.