Unless somehow all thr spoilers are true! But if they are then.... DAMN Stephenie has been lying to us about a lot of stuff!!!

The first "quote" is from IMDB, the second from Twilight Lexicon. Stephenie has approved both of these websites - so I think we can trust the info they give us to be fact.

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Can vampires have babies? What happens when a woman is pregnant and gets changed?
No. In the Twilight universe, a vampire's only bodily fluid is its venom; this replaces the saliva and other fluids. Thus, vampires have no sperm, so they cannot make vampire babies. When a human is changed into a vampire, they are essentially "frozen" and thus will stay same way forever. If a pregnant woman is changed, she will remain pregnant forever, no matter what stage her pregnancy was in, two days or eight months, and the baby will never be born.

This also explains Alice's hair. Before she was changed, she was in an asylum, so her hair had been shaved off, and it was just growing back when she was changed. If you have long hair and you are changed, but then you cut that hair, it will not grow back. They can style their hair, though, such as getting hair extensions or using curling and straightening irons.

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No further physical changes occur once someone has been transformed: "When someone becomes a vampire, it’s as if they are frozen exactly as they are in that moment." (PC1) Therefore, a vampire cannot get pregnant because this would involve a change in physical state, but if a pregnant woman were changed to become a vampire, then she would remain at that exact stage in pregnancy for all eternity.

Natural changes in the human body would not occur any longer. A woman would "no longer have any kind of ovulation cycle," (PC1), a man would no longer need to shave as hair would no longer continue to grow. Once cut, hair will never grow back, and we are given the example of Alice, whose hair is so short because "it was growing back from being shaved in the asylum." (PC1). Alice will never be able to have the long flowing locks of Rosalie.