you can't get pregnant, you're two different species, it's like a bear mating with a wolf. second there are risks when dealing with any type of spirit/demon/astral being. an incubus is a demon who gains energy from the act of sex. once and a while summoning one [done correctly] you probably won't get hurt, but constant encounters can leave a human weak and tired, they might become sick, and in a few cases apparently have died. while i don't get why you'd want to summon one [i mean, i know why, but i don't get the appeal] think before you do.
The incubus, or succubus, is the medieval explanation for sleep apnea, sleep paralysis, "wet dreams" and other sleep disorders. When they exist at all in our world is in the same sense that a thoughtform or servitor exists in our world - they are a manifestation of our subconscious and will, typically of the one fantasizing or frightful of them.
This kind of creature is just a projection of your ow desires. The energy that you spend thinking in someone (sexually, of course) can made this kind of being.
By the way, there is some psychic vampires that drain your life energy making "sex" with you. Inducing an orgasm (wich is something VERY powerfull) the vampire drain the energy.
Both cases are very harmful to your health. There is NO SAFE WAY to live with this kind of being. The best that you can do about them is to protect yourself and your loved ones.