If vampires don’t have any body fluids, then how did Bella become pregnant in the Twilight series?
As stated by other people, vampires do have bodily fluid such as venom and maybe more-of which we’re not aware. Venom in Bella’s eyes dissolves the artificial pigment on her eyes in ‘Breaking dawn’ which is a corroboration to the above stated fact.
Also, it’s imperative to mention that Twilight Saga is a young adult fantasy and romance novel series so it’s absurd to try to contrive some biologically valid explanation for this happening. Albeit I agree that author always tries to make things as much logical as possible for simple minds, it would never be enough if you try to take a scientific stance. So let’s have a simple approach – hold on to it – and delve into explanation.
It has been explicitly mentioned that vampire’s cells can’t divide or replicate so they don’t age and stay the way they are forever. That’s simply the reason why female vampires can’t bear a child because female body need to constantly undergo changes to accommodate the foetus. Men are, however, biologically same once teenage is over, except for the aging which stops even in male vampires.
Now, since a man is capable of reproducing till his death, male vampires have sperm in whatever complexion it maybe.
We know that vampires have two extra pairs of chromosomes i.e. 25 pairs while have 23 pairs. It’s interesting to note that shapeshifters(Quilette tribe ones) have 24 pairs of chromosomes as mentioned by Carlisle in Breaking dawn. Now, when a vampire sperm having 25 pairs of chromosomes fertilises a human ovum having 23 pairs of chromosomes, they form a zygote having 24 pairs of chromosomes – which, not surprisingly, is same as shapeshifters. Thus, having such chromosomal similarity with shapeshifters is what enables Renesmee to perform feats which are otherwise impossible for vampires.
Since shapeshifters grow old naturally but have the ability to freeze their aging at will, Renesmee too has the ability to grow(unlike other vampires) at will, which is why Renesmee grows so fast, and will stop aging once she’s old enough. We have proof for it as well. Nahuel was first known vampire human child and he stopped aging once he was old enough.
This, again, may be the reason why Renesmee’s bites didn’t kill Jacob as she’s not venomous. If she was venomous, her bites should have killed Jacob seeing as vampire venom is lethal to shapeshifters. Mind you – this is somewhat contentious as Nahuel is venomous while his sisters are not. It has also been posited that female vampire human children might not be venomous but there is no canon explanation.
After all, there are always some loopholes(It’s fiction) but if you try to see simply without deliberately trying to find something, it will make sense. Importantly, since original reasons aren’t mentioned in the books, I have used simple inductive reasoning to explain the scenarios. Ergo, I maybe woefully wrong – though I don’t think I am.