27 percent of women who missed two pills in a row risked pregnancy

January 22, 2007
  • umichnews@umich.edu

ANN ARBOR— A pill a day keeps the obstetrician away. The trick is to remember to take the pill or to use back up contraceptives for seven days if you forget.

Despite the seeming simplicity of birth control pills, 27 percent of women in a contraceptive use study didn’t take the pill for two or more consecutive days and used no backup contraceptives in the following week, so they were at increased risk of pregnancy. Also, half of those women missed two or more pills at least twice during the three-month study.

The study of 103 women in Michigan and North Carolina was conducted by researchers at the University of Michigan School of Nursing and Family Health International, a research firm in Research Triangle Park, N.C. Their findings are reported in the November/December issue of Family Planning Perspectives. About 18 million U.S. women take the pill.

According to electronic devices that recorded the time and date that each pill was removed from the blister pack, 52 percent of the women took each pill or never missed more than one pill at a time after the first week of the initial cycle.

Eighteen percent of the women missed two or more consecutive pills but modified their risk by avoiding intercourse for the next seven days, while another 3 percent who missed pills protected themselves by using backup contraception such as condoms for the next seven days.

“We found that demographic and most psychosocial characteristics were not related to women’s consistent use of the pill. However, we did find that the number of days that a woman had intercourse was a factor in elevated risk,” said Deborah Oakley, U-M professor of nursing and principal investigator.

Women who were never at risk had intercourse, on average, on 11 days during the study while women who missed two pills had intercourse, on average, on 22 days. “The combination of two missed pills and more frequent intercourse elevated their risk considerably,” Oakley noted.

Women who missed two pills also were more likely to have had unprotected intercourse in the first seven days of the initial cycle?a high risk period during which hormonal levels are still too low to protect women from pregnancy?and during the third pill cycle.

“Women who felt they did not have their partner’s support for taking the pill, unmarried women and women who did not feel it was important to avoid pregnancy now also were more likely to miss pills,” she added.

Society also makes it difficult for women to use the pill. “Some HMOs allow women to buy only one month’s supply of pills at a time,” she explained. “It requires immense logistic acumen to obtain refills during the one-week window allowed toward the end of the cycle.”

In addition, Oakley recommended that women who are traveling be allowed to purchase pills at multiple pharmacies or at least pick up a few pills to carry them through the trip.

Oakley is also conducting research on contraceptive behavior in China, and has found that women there are more likely to miss a pill when there is chaos in their lives or they are coping with a highly variable schedule.

“Chinese women who were starting up a business or had to change shifts at work were more likely to miss a pill. We suspect that lack of routine in daily life schedules can affect American women’s behavior as well,” Oakley said.

Why is it important that pharmacies and health care providers make it easier for women to obtain their prescribed pills?

“Almost 50 percent of all U.S. pregnancies are unintended and, among abortion patients, about 58 percent became pregnant while on the pill,” Oakley said.

Oakley’s colleagues on the study were Linda Potter, now a visiting research scholar at Princeton University, and Emelita De Leon-Wong and Cynthia Visness, researchers at Family Health International.

U-M News and Information ServicesUniversity of Michigan