Vertical and Horizontal Clitoral Hood Piercings
First of all, the vertical/horizontal misunderstanding needs to be cleared up. If a woman decides she wants a clitoral hood piercing, it is normally not her decision as to which one she will get. A skilled piercer, upon examining the clients genital area, will recommend one piercing over the other for proper placement and the best fit. In very rare cases, some women may be anatomically suited for either piercing and can make that choice at their own discretion.
Will a clitoral hood piercing stimulate the clitoris during sex? Maybe. That depends on the skill of the piercer and the body of the pierced. If the woman received the correct piercing (vertical or horizontal) for her particular anatomy and the piercing was done properly to encourage clitoral stimulation, then it should enhance pleasure during sex.
Can a woman lose her ability to achieve orgasm if she gets her clitoral hood pierced? No. Sexual stimulation comes from the clitoris itself, not the clitoral hood, which is just a protective fold of skin that goes over the clitoris. If a woman gets a horizontal or vertical clitoral hood piercing, it will not affect her ability to have an orgasm.
Piercings that actually penetrate the clitoris are much more risky than hood piercings. A potential client must be examined by a professional piercer to first see if she is even anatomically suited for a clitoral piercing. The procedure can be painful, as it goes through many nerves the same nerves responsible for sexual response. In rare cases, it is possible for a woman to lose her ability to achieve orgasmic climax or even lose all feeling as a result of a clitoral piercing. Granted, this is a worst-case scenario, but only a highly skilled professional piercer should perform a clitoral piercing.
Labia piercings, although they may be visually arousing to your partner, will not affect your own sexual pleasure. They are not located close enough to the clitoris to cause stimulation, and are more for aesthetic pleasure.