Follicular Waves

In 2003 a University of Saskatchewan research team funded by the Canadian Institutes of Health Research uncovered evidence suggesting that the traditionally accepted model of the human menstrual cycle is wrong. This discovery, initially published in the scientific journal Fertility and Sterility, may lead to the design of new, safer and more effective contraception, and may improve success with assisted reproductive technology for women who are having trouble conceiving. Dr. Roger Pierson, head of the university’s Reproductive Biology Unit, received the 2003 Women’s Health Hero Award from Chatelaine magazine for the discovery; in addition, Discover magazine ranked the results among the top 100 science stories of the year.

Previous research had shown that a group of 15–20 follicles grew during the menstrual cycle, and that one follicle from the group was selected to ovulate while the others died off. The new research found that this process occurs in waves: in response to hormone surges, women experience two to three periods of follicular development each month, although only one egg is selected for ovulation. As a result, it is estimated that up to 40% of women may not be able to use natural family planning methods: for women who experience two or three waves of dominant follicle growth per month, there is no “safe” time to have intercourse during the cycle, as there may always be a follicle capable of ovulating. The study, involving sixty-three women with normal menstrual cycles who underwent ultrasound every day for a month, was the culmination of a long-term collaboration between Roger Pierson, veterinarian Gregg Adams, and biologist Angela Baerwald.