Vampire/Human Hybrid

A human-vampire hybrid, also known as half-vampire, vampire hybrid, half-human and half-vampire, and half-immortal, is the offspring of a female human and a male vampire. It is generally beyond the ability of most vampires to be this close to a human physically and still resist the lure of her blood. Human/vampire hybrids are therefore an extremely rare occurrence.

Conception
The whole process is extremely risky and can easily fail due to the fragile human body.

A hybrid is conceived by the sexual intercourse between a female human and a male vampire. Because most vampires have a hard time resisting the urge to kill humans, it takes a high level of self-control to be so close to the human and still resist the temptation of her blood.

Once the woman is impregnated, the fetus inside her grows much faster than human fetuses, and will grow extremely strong overtime. Should it cause too much trauma to her before birth, it can easily destroy its own existence by killing the mother. If the fetus is not often fed with blood, it will involuntarily deteriorate its mother's health, making the chances of survival even smaller.

The fetus is grown to full term one month after conception, and will utilize its own strength and teeth to break its way out.

Physiology
Vampire hybrids have both human and vampire traits.

They are immensely beautiful. Due to their beauty and superhuman abilities, they can be mistaken for immortal children by other vampires who see them from a distance when they are still maturing. They have well-developed physiques and smooth, flawless skin, which is paler than a human's but not as pale as a vampire's.

Unlike vampires, they have a functioning heart with blood flowing through their system. A hybrid's beats faster than a human's. They are capable of sleeping like humans and of eating and gaining nourishment from both human food and blood, though they prefer blood, particularly human. Their body temperature is unusually warm, just a few degrees below that of shape-shifters.

While vampires are unable to take the sunlight without he assistance of a day ring, hybrids suffer no harm from the suns rays.

Hybrids possess the mixed scent of vampires and humans. This gives them a unique scent all their own, balanced between being both appetizing as a human's and sweet as a vampire's. Bella Swan described this as just enough vampire scent to keep the human scent from being too overwhelming.

They have 24 chromosome pairs, but it is unknown whether this is due to a sampling error or chromosome rearrangement. It seems, however, unlikely that they have any relation to the shape-shifters' chromosomes.

As with shape-shifters, hybrids are a blind spot in Alice's vision. This is later explained to be due to the fact that Alice has never experienced life as a shape-shifter or a hybrid, and therefore cannot relate to it.

Hybrids are able to reproduce.

Development
Vampire hybrids grow at an unprecedented rate during their early lives, reaching full physical maturity at about seven years of age, with an apparent biological age of their late teens. At this point their development will then cease altogether, reaching the same state of full vampires.

Powers and Abilities
They are supernaturally much stronger and faster than humans, with sharper senses, but are not as strong, fast, or sharp as a pure vampire. Like the hybrid's amniotic sac, her/his skin is almost as durable as a vampire's. They have perfect memory recall and develop mentally at a rate far faster than their chronological and biological age, speaking in complete sentences and walking just days after birth.