Victoria Jennings -- a professor of obstetrics and gynecology at Georgetown University Medical Center Institute for Reproductive Health at Georgetown University Medical Center -- said the Standard Days Method identifies the 12-day "fertile window" of a woman's menstrual cycle, taking into account the life span of an egg, 24 hours, and the viable life of sperm, about five days.
The researchers tracked study participants for three years. An earlier study that tracked women for one year found the new method was more than 95 percent effective at avoiding pregnancy -- higher than a diaphragm or condoms.
The Institute for Reproductive Health developed CycleBeads, a string of 32 color-coded beads with each bead representing a day of the menstrual cycle.
Beginning with the red bead, which represents the first day of her menstrual period, a woman moves a small rubber ring one bead each day. The brown beads are the days when pregnancy is very unlikely, and the glow-in-the dark white beads -- beads 8-19 -- represent her fertile days, Jennings said.
The study, scheduled to be published in the October issue of the Journal of Family Planning & Reproductive Health Care, found the multi-country three-year study of 1,659 women indicated women are likely to continue to use the method, and to use it effectively.