When a female enters puberty, that is a time to discuss issues like abstinence, or safe sex practices. The idea is not to have a child while the female is still a child herself. As females mature, there are other things that many of them would rather do than have children. They want to have the romantic relationships, but they also want to focus on their careers, etc. So, as a form of birth control, they have their fallopian tubes blocked.
Many women have their fallopian tubes blocked with the idea that eventually they will have the option of getting tubal reversal. This is a procedure wherein the surgeon, using microscopic tools, unblocks the fallopian tubes, thereby allowing the woman to become pregnant again.
In order to understand how tubal reversal works, it is important to understand how conception takes place. A man's sperm needs to travel up the female's fallopian tubes to meet the egg, fertilize it, and conceive. Blocked fallopian tubes will obviously not allow this to happen. However, once tubal reversal is done, many women become pregnant within three months of having the procedure.
Tubal reversal is something that is ideally done only a couple of years after the initial procedure. This is because the fallopian tubes will be more amenable to the procedure, which obviously produces the best results. The age of the woman is also something to consider, but since each woman is different, only an examination of the reproductive system could find out the chances for conception for sure.