|Source: Ceridwen, Wikimedia Commons|
In the 20th century, contraception reached the woman's control again with the advent of hormonal contraception - the birth control pill. Rather than relying on the spermicidal effects of chemicals, the pill alters the levels of hormones in a woman's body, redirecting, or sometimes altogether preventing, ovulation. Basically restricting the body's ability to conceive.
In the last half century, synthetic hormones and combinations have been tested and marketed in order to fine tune the process, achieving as high as 99% reliability when used properly, as well as eliminate side effects, which can include cardiovascular problems and female cancers.
Each woman can decide just how she wants to control her ability to conceive - see WebMD for a list of available types, along with their pros and cons.