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2003/11/27
They have called for urgent
research into some systems, which help couples follow "natural family planning" methods
avoiding active contraception.
A variety of methods are used
to spot changes which suggest a woman is approaching her "fertile
window". But German experts said, in the journal Human Reproduction,
that using some, more than half of readings were wrong.
They
say this could lead to unplanned pregnancies in the absence
of any other methods of birth controls.
Professor Guenter Freundl,
from the Department of Reproductive Medicine at the Staedtische
Kliniken Dusseldorf, said: "If a couple are going to rely on
these monitors, especially for contraception, then it is extremely
important that they have reliable information about the effectiveness
and accuracy of the different systems."
The findings from 62
women and their monitors in their preliminary study, he says,
already mean that some do not meet a minimum quality standard
and should not be offered to women.
These included systems
involving a mini-microscope, which rely on the user recognising
a particular pattern in small samples of their cervical mucus
or saliva.
The three systems tested registered "false negative" rates - in which the woman
believes she is not fertile that day, when in fact she is - in 51.8%, 58% and
73.4% of tests respectively.
Better temperature
Other methods were more reliable.
One involving temperature tests in combination with changes in cervical mucus
composition - often taught by instructors to women, gave no false negatives among
the 15 women using the method.
Secretions become heavier and change in texture
around ovulation - the time of the month when an egg is released ready for fertilisation.
Another body temperature method involving a mini-computer to record and store
the data produced between 1.7% and 7.5% false negatives.
Finally, a urine hormone
test managed 20.8% false negatives.
Professor Freundl said: "This meant that the symptothermal method of NFP that
relies on a woman's own observations proved to be the most effective of the natural
family planning methods.
"But, the mini-microscopes had a very low estimated
efficacy."
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Contraception