About half of all unintended pregnancies occur among women using contraceptives (Frost & Darroch, 2008). Unmarried women younger than 30 years old are most likely to have a contraceptive failure, and married women older than 30 are least likely to do so. In addition, low-income women experience greater failure rates than more-affluent women, possibly because of limited availability of health care (Fu et al., 1999).

Under various circumstances, a couple may need or want to use backup methods— that is, more than one method of contraception used simultaneously. Condoms, contra­ceptive foam, and the diaphragm are possible backup methods that can be combined in many ways with other birth control methods for extra contraceptive protection (Peipert et al., 2011). Circumstances in which a couple might use a backup method include the following:

■ During the first cycle of the pill.

■ For the remainder of the cycle, after forgetting to take two or more birth con­trol pills or after several days of diarrhea or vomiting while on the pill.

■ The first month after changing to a new brand of pills.

■ When taking medications, such as antibiotics, that reduce the effectiveness of the pill.

■ During the initial 1 to 3 months after IUD insertion.

■ When first learning to use a new method of birth control.

■ When the couple wants to increase the effectiveness of contraception (for instance, using foam and a condom together offers effective protection).