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WASHINGTON, Oct. 31, 2003
"No
wonder the rhythm method does not work so well for birth
control„ - scientists in Canada said Tuesday they had found
women sometimes ovulate several times a single month.
Their
findings, if verified, would overturn the traditional wisdom
that women produce an egg cell once a month. It would also
help explain why ñnaturalî 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 womanÍs 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 donÍt 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,î 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 10 weeks development and another at seven."
Copyright 2003æReuters Limited
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