By Maggie Fox, Health and Science Correspondent WASHINGTON (Reuters)
- No wonder the rhythm method does not work so well for
birth control -- scientists in Canada said on Tuesday they had found
women
sometimes ovulate several times a single month.
Their finding, if verified, would overturn the traditional wisdom that
women
produce an egg cell once a month. It would also help explain why "natural"
methods of birth control, based on the idea that ovulation can be predicted,
often fail.
"We are literally going to have to re-write medical textbooks,"
said Dr.
Roger Pierson, director of the Reproductive Biology Research Unit at
the University of Saskatchewan, who led the study.
"It's exactly why the rhythm method doesn't work."
Scientists have long known that humans have unique cycles of ovulation.
Many animals come into heat -- a time when all the males around know
through smells and visual signals that a female is ovulating and ready
to
conceive.
Not so with humans, who have "concealed" ovulation. Standard
medical science says a woman has a cycle running roughly 28 days in
which an egg ripens, is released by the follicle, drops into the fallopian
tube, and then is either fertilized or shed during menstruation.
Writing in the journal Fertility and Sterility, Pierson and colleagues
found this did not always happen.
"We weren't expecting this. We really weren't," Pierson said
in a telephone
interview.
DAILY ULTRASOUND SCANS
In the study, Pierson, veterinarian Gregg Adams and graduate student
Angela Baerwald did daily, high-resolution ultrasound scans on 63 women
for a month, which allowed them to see the follicles very clearly.
"We had 63 women with normal menstrual cycles. Of those 63, only
50 had normal ovarian cycles," Pierson said.
Thirteen of the women ovulated multiple times, in various different
ways. And of the other 50, 40 percent had up to three waves of activity
by
the follicles, any one of which could result in the production of an
egg.
The women's hormone levels did not match this activity, Pierson said.
"Hopefully this will help women explain how they got pregnant when
they
really didn't want to be pregnant, and it certainly will help us design
better fertility therapies."
Apparently, measuring hormones in the blood is not enough to predict
what a woman's reproductive system is up to.
"The hormones do what they are going to do and the ovaries just
follow
their merry path," Pierson said.
"We always thought that menstrual cycles and ovarian cycles were
one
and the same. It turns out they are just like two political parties
-- sometimes
they go along hand in hand for the good of the country and sometimes
they go along their separate ways."
Pierson's team plans longer-term studies to see if the women's patterns
are consistent from month to month.
"We don't know what's causing it -- we don't know if it is the
weather
or exposure to men or grapefruit juice or what," Pierson said.
The findings, which were first seen in cattle and horses, help explain
some things that have puzzled obstetricians, Pierson said.
"It really explains how we get fraternal twins with different
conception
days," Pierson said. "Clinically, we see this all the time.
We see women
come in with twins and when we do an ultrasound we see one is at one
10
weeks development and another at seven."