Research suggests third of ovulations eggless
Evolutionary factors could be the cause
For women hoping to get pregnant, having a regular, normal-length period is no guarantee they are actually ovulating, according to Canadian researchers who say one-third of all seemingly normal menstrual cycles may be egg-less.
Their new study suggests “silent anovulation” — where a woman has what appears to be a regular cycle, but the ovaries release no egg — is much more prevalent than previously believed.
“There is a medical/cultural expectation that clinically normal menstrual cycles are inevitably ovulatory,” the team writes in the science journal, PLOS ONE. “The presence of silent anovulation in over a third of clinically normal menstrual cycles within a large population appears to mandate a new understanding of women’s reproductive physiology.”
Other experts, however, says the researchers are wildly overestimating the problem.
Anovulation is caused by unhealthy hormonal imbalances that threaten a woman’s fertility and increase her risk of bone loss, early heart attack and breast cancer, said lead author Dr. Jerilynn Prior, a professor of endocrinology at UBC and scientific director of the Centre for Menstrual Cycle and Ovulation Research.
Stress is one of the most common causes and the researchers believe not ovulating is actually an evolutionary response to prevent women from getting pregnant “when our lives are in turmoil,” according to background material released with the study.
“I see ovulatory disturbances as a finely tuned adaptive response to a whole suite of stressors,” Prior said in an email interview. Women require more energy (calories) during pregnancy, energy that is in short supply if the woman is already emotionally stressed, under-eating, over-exercising or experiencing other stressors.
“It’s also protective for the whole ‘tribe’ since, for example, if they needed to migrate, they wouldn’t have the increased calorie or health risks related to pregnancy or a newborn,” she said.
Earlier studies found that only about four to 10 per cent of healthy, premenopausal women do not release an egg during a cycle. “That’s as prevalent as anyone previously thought anovulation could be,” Prior said.
Women normally have a 28-day menstrual cycle. Most ovulate, once, around Day 14. Theoretically, if a woman isn’t ovulating, she should not be bleeding.
Normal levels of estrogen and progesterone are needed for ovulation. Progesterone is high only in the second half of the cycle, when the egg is released. One of the best ways to determine if an egg has actually been released is the rise in progesterone that occurs in the second half — the luteal phase — of the cycle.
The new study is based on more than 3,000 women aged 20 to 49 living in rural Norway who were tested once during one regular, normal-length menstrual cycle.
Thirty-seven per cent of the women who had had blood drawn at cycle day 14 or higher had progesterone levels below the threshold needed to ovulate.
What the researchers can’t know from the single-cycle study, in which women were tested only once, is how many of these women will be “perfectly normally ovulatory” in their next period, Prior said. Another major limitation is that the average age of the women in the study was their early 40s.
But Prior worries too few women with seemingly normal periods who see a doctor for problems related to infertility — for example, no pregnancy after a year of trying— are tested to determine whether they’re actually ovulating normally.
Doctors can order progesterone tests that cost about $40 to check for anovulation, which can be treated with progesterone therapy, Prior said.
“Regular, normal-length menstrual cycles are not a guarantee of normal ovulation,” she said.
“It’s also important for women and doctors to realize that emotional, social or physical abuse, or illnesses, including mental or emotional ones, cause changes that are body-wide,” she said. “They need to be faced, understood and dealt with to restore optimal fertility and normal hormone balance.”
But fertility experts questioned the findings. “You can’t assume that everyone is going to ovulate on day 14,” said Dr. Neal Mahutte, president of the Canadian Fertility and Andrology Society.
Progesterone is a moving target, he said. “If you sample somebody’s blood around the time of ovulation, or a day after they’ve ovulated, the progesterone isn’t at its peak,” he said. “It’s on the rise.”
“It wouldn’t surprise me at all if the vast majority of people who got tested on Day 14 had levels” below the threshold for ovulation. “It’s really only when you get to the middle of the luteal phase that you expect these high levels of progesterone.”