"To really examine how incredibly messed up this is for Amy as a character, you have to look at how River is introduced. In the previous Doctor’s tenure, once Moffat had been named the future show runner, he introduced a woman called River Song, who was The Most Important Woman That Will Or Has Ever Existed To The Doctor, but she couldn’t reveal why because she was meeting him out of order (curse of the time traveller). The next season, Amy is introduced.
The main purpose of Amy Pond was always for her to be the mother of the magical child who would be both the Doctor’s Girlfriend and Ultimate Foe. This was Moffat’s long game. Her relationship with the Doctor was predestined not because of her own, unique self but because of what would be in her uterus. And Steven Moffat expects us to think this is the most amazing plot twist ever in the near fifty-year history of Doctor Who."