EUGENE, Ore. -- A surprisingly large number of women 18 or older choose to delay or skip monthly menstruation by deviating from the instructions of birth-control pills and other hormonal contraceptives, a team of University of Oregon researchers and others found in a study of female students at the university.

Most women who alter bleeding cycles do so for convenience rather than to avoid menstrual symptoms, and many learn about the option from nonmedical sources, according to research by the university's Department of Human Physiology, Portland-based Oregon Health and Sciences University and Eastern Michigan University. The study is published in Contraception, the official journal of the Association of Reproductive Health Professionals and the Society of Family Planning.

"These findings emphasize the need for health care providers to carefully interview combined hormonal contraceptive users on how they are using their method - for example, many women may be skipping pills to extend their cycles," said researcher Christopher Minson, a human physiology professor at the University of Oregon. "With a greater understanding of the issues, health care providers may be able to more effectively engage in conversations with college-aged women and educate them about available options."

As research indicates that reducing the occurrence of menstruation is safe and can even be beneficial, women are increasingly using hormonal contraceptives to alter bleeding cycles. But there has been a lack of information concerning why women do so and from whom they receive information regarding this option.

In a survey of undergraduate and graduate students, 17 percent reported altering their scheduled bleeding pattern by deviating from the instructions of hormonal contraceptives, which include birth-control pills, vaginal contraceptive rings and transdermal contraceptive patches.

Half of these women reported that they did so for convenience or scheduling purposes. Others cited personal preference (28.9 percent) or reducing menstrual symptoms (16.7 percent) as reasons they altered menstruation patterns.

Among the women who delayed or skipped a scheduled bleeding for convenience or personal choice, a comparatively large number - 53 percent - indicated the knowledge was obtained from nonmedical sources, such as a family member or friend, researchers said.

The survey also provides new insights on the factors that influence a woman's decision whether to alter bleeding schedules. Asians have a 7 percent lower probability of altering hormonal cycles and women who exercise regularly have a 5 percent lower probability of doing so; another characteristic that decreased the likelihood of the practice was preference for a monthly cycle.

"We found that it is possible to identify some of the specific characteristics of women in a college population who may be more or less likely to practice scheduled bleeding manipulation," said Dr. Paul Kaplan, of the University Health Center and Oregon Health and Sciences University. "This study provides information about the motives, beliefs and influences relating to this practice."

In a finding that surprised researchers, women who said they would prefer no menstrual periods were less likely to alter their cycles than those who would prefer one per year. A woman who would prefer one cycle per year had a 17 percent higher probability of modifying her hormonal contraceptive regimen than one who preferred a menstrual period every three months or never.

This suggests that health care providers could improve education of the hormonal contraception regimen best-suited to a patient's needs and desires, researchers said.

From an estimated 11,900 survey-linked emails sent to female university students, 1,719 (14.4 percent) initial responses were received and 1,374 (79.9 percent of respondents) indicated that they had used a combined hormonal contraceptive during the last six months.

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The National Institutes of Health supported the research with a grant (5R01HL081671) from the National Heart, Lung and Blood Institute.

About the University of Oregon

The University of Oregon is among the 108 institutions chosen from 4,633 U.S. universities for top-tier designation of "Very High Research Activity" in the 2010 Carnegie Classification of Institutions of Higher Education. The UO also is one of two Pacific Northwest members of the Association of American Universities.

SOURCE: Christopher Minson, professor, Human Physiology, 541-346-4105, minson@uoregon.edu

Note: The University of Oregon is equipped with an on-campus television studio with satellite uplink capacity, and a radio studio with an ISDN phone line for broadcast-quality radio interviews.