The final book in the Twilight series, Breaking Dawn, saw Bella and Edward starting their own family – but readers and viewers have wondered how it was possible for Edward to get Bella pregnant. In 2005, Stephenie Meyer introduced readers to a world where humans, vampires, and werewolves coexist in Twilight, the first in a series of four novels that chronicled the problematic romance between vampire Edward Cullen and mortal Bella Swan, with werewolf Jacob Black in between.
Bella and Edward’s story came to an end in Breaking Dawn, where the young couple got married and started their own family with the birth of their daughter, Renesmee, and Bella’s conversion. Although vampires in Meyer’s world have a couple of differences from these legendary monsters, such as sparkly skin and eye-color that changes, they retained their most basic characteristics, like immortality and drinking blood to live. Taking that into account, it was quite surprising that Edward got Bella pregnant (and that’s without counting everything that happened during the pregnancy), and that’s one of the biggest questions viewers have had for years.
As vampires are undead creatures, no fluids run through their bodies, so it would be physically impossible for one to get pregnant or get someone else pregnant. It would be especially impossible in the Twilight universe given that the skin of vampires is described as hard as stone, and even having sex with Bella was dangerous as Edward could unintentionally kill her. Still, Bella got pregnant during her honeymoon and gave birth to a vampire/human hybrid, and after being asked the same question over and over again at any given chance, Stephenie Meyer explained how that part of the Twilight world works... and it still doesn’t make much sense.
According to Meyer, vampires are still “physically similar enough to their human origins” so they can pass as humans in most circumstances – the trick is in their cells and other fluids. Meyer explained that the cells that form their skin are “not pliant like our cells, they are hard and reflective like crystal”, and a fluid similar to the venom in their mouths (the one that helps them turn humans into vampires) serves as a “lubricant between cells” and is very flammable, hence why these vampires can be killed by burning them. Through a vampire’s body are other fluids similar to that venom that have similar functions to those when they were humans (like lubricating the eyes, for example), and some carry many of the functions of blood. Their bodies, then, can react to certain emotions and sensations like a human body, and that includes reactions of arousal.
Meyer’s explanation continues and solves the second part of the mystery: according to her, there are “fluids closely related to seminal fluids” in the bodies of male vampires, and these fluids carry genetic information. These can totally bond with a human ovum, which Meyer adds wasn’t a known fact within Twilight’s vampire world before Renesmee’s birth. This basically means Edward’s body is powered by venom, which makes Bella’s pregnancy even more dangerous than it already was. Of course, this detailed explanation wasn’t enough for some, and there are still many questions about it, but Meyer built her own mythology in Twilight, and there’s not much to do than accept it, even if more often than not it doesn’t make sense.