Discovery may rewrite book on human menstrual cycle

TORONTO (CP) -- Saskatchewan researchers have made a discovery that could force the rewriting of text books on the female menstrual cycle, which could in turn lead to better infertility treatments, oral contraceptives and fewer "oops" babies.

The team, based at the University of Saskatchewan, discovered that many women actually have the potential to ovulate more than once per cycle, a finding that challenges the dogma on the human cycle.

"A significant portion of the population has either two major waves or three major waves during the cycle and that means they have the potential to ovulate at any one of those three times," said Dr. Roger Pierson, lead author on the study, which is published in the current issue of Fertility and Sterility.

"They might not necessarily ovulate because other hormones are keeping the signal from the brain from getting to the ovaries.... But life happens and there isn't always perfect control."

The findings could help to explain a number of the mysteries about conception: why the rhythm method is such a lousy form of birth control; why oral contraceptives don't work for some women and why some women can be impregnated very early or very late in their cycles, for instance.

They may also point to ways to improve the rather dismal success rates of in vitro fertilization techniques, said Dr. Bruce Murphy, a professor of reproductive biology at the Universite de Montreal.

"It could radically improve the success of this super-ovulatory treatment," said Murphy, referring to the treatment in which women are induced through drug therapy to produce more than one egg for IVF purposes.

Murphy called the findings "quite convincing."

"To me it's quite solid and I think it will be accepted," he said.

While Murphy was not involved in the research, he is on the advisory board of the Canadian Institute of Health Research's Human Development and Child and Youth Health Institute, which funded the study.

Pierson and his co-authors studied a group of 63 women, aged 18 through 40, with normal menstrual cycles. Some had had as many as four children, while others had had none. For this type of research, this sample size is quite large, both Pierson and Murphy said.

All the women underwent a trans-vaginal ultrasound every day for about six weeks, allowing the researchers to get a clear picture of the activity of the ovaries over the period of a full menstrual cycle.

For nearly 50 years, Pierson explained, science had thought it knew how the ovaries worked. The school of thought evolved from the study of hormone levels in blood and dissection of ovaries removed for medical reasons.

The thinking was that once a cycle a group of 15 to 20 follicles -- fluid-filled sacs containing an egg -- would develop. One, through a process that is not understood, would become dominant and would develop to a point where release of the egg -- ovulation -- could occur, on or around Day 14 of a 28-day cycle. (Ovulation doesn't always occur; sometimes a follicle will regress and die without releasing its egg.)

But the ultrasound pictures told another story.

Instead of one long wave of follicular development, women underwent two or three waves of development during their 28-day cycle.

Most of the women -- 50 of the 63 -- had normal ovarian cycles and none of these women ovulated more than once during the period of study. But about 40 per cent of them also developed a dominant follicle during one of the waves that didn't lead to ovulation, Pierson said, suggesting that under the right circumstances they could have ovulated twice in a cycle.

Thirteen of the women had abnormal ovarian cycles. Of this subgroup, two women actually ovulated twice in a cycle, noted Pierson, a reproductive endocrinologist and director of the university's reproductive biology research unit.

The researchers also found that some women ovulated as late as Day 21 of their cycle -- a finding which explains why Day 14 can't be reliably assumed to be the magic time to have or refrain from sex, depending on whether you want to get pregnant or are desperate not to.

"What it tells us is there's this broad span of biological variation and that this text book-like cycle just doesn't exist," Pierson said.

"That's why we've got to really think about changing the way we're teaching people about the menstrual cycle."

Pierson said the findings should have implications for IVF techniques and oral contraceptives. For women who can't rely on oral contraceptives, "it's the biological foundation for why those problems occur."

"Certainly when we think about women undergoing fertility therapy, we're going to have to consider different times for different drugs and different types of drugs," he added.