First, here’s a quick 101 on vampire biology from Meyer:
“Vampires are physically similar enough to their human origins to pass as humans under some circumstances (like cloudy days)…The skin serves the same general purpose of protecting the body. However, the cells that make up their skin are not pliant like our cells, they are hard and reflective like crystal. A fluid similar to the venom in their mouths works as a lubricant between the cells, which makes movement possible (note: this fluid is very flammable)… Throughout the vampire’s body are many versions of venom-based fluids that retain a marked resemblance to the fluid that was replaced, and function in much the same way and toward the same purpose…Though there is no venom replacement that works precisely like blood, many of the functions of blood are carried on in some form.”
Meyer has an answer for that too.
“Like with vampire skin—which looks similar to human skin and has the same basic function—fluids closely related to seminal fluids still exist in male vampires, which carry genetic information and are capable of bonding with a human ovum.”
TL;DR Edward’s jizz is venom.
This has been vampire sex ed with Stephenie Meyer and me.