This is actually a more general question about vampires, but it also happened in Underworld 3. Apparently, Lucian and Sonja fell in love and then she became pregnant. But is this possible? The way I see it, vampires have a dead body, so how is it possible to have a well working reproductive system? When a human is turned into a vampire, he considers the one who turned him as him family or at least his tutor. I consider this a major plot hole in all such movies am I right, or have there been references that such a thing is possible?
Vampires in the Underworld universe aren't undead as far as I know. As with the Lycans they're essentially just infected by a special mutated strain of the plague. This grants them a lengthened lifespan as well as a massive potential for regenerating their bodies (essentially keeping them alive). If they'd be undead, they would stop aging or growing, which apparently isn't the case, considering Selene has been infected as a kid.
The issue with stories about vampires is that they're open to interpretations and each author/universe changes their rules.
The three most common types of vampires are
- Undead humans (the oldest, classic style)
- Infected humans (a more sci-fi take)
- Demons (more recent)
Of those three, only the Undead humans would, in theory, have a non-functioning body. But even those rules are iffy. Which parts work or don't? You can't breathe or talk without working lungs. You can't get an erection without a working heart.
In addition to Underworld, at least Twilight and Angel have had vampires who became pregnant. Though, it should be noted that even according to the rules in Buffy/Angel, pregnancies in vampires should not occur, and it was only due to magic that it did.
I see your point, though let’s note that Underworld vampires actually have a working, living body. They have flowing blood, as we can see when Selene bites her wrist to reawaken Victor. Speaking of which, when she gives Victor her blood, we see it run through his system and start up his heart, which begins to beat. So they clearly have a circulatory system, and, as Rise of the Lycans and Awakening has shown us, a well functioning reproductive system, and everything else humans need to survive. Unlike Twilight or Interview with a Vampire, Underworld vampires are not undead, they are infected with a rare version of the Plague. Bearing this in mind, we can infer that these vampires can perform everything a human can (albeit on a far more superior level), which includes having a baby.