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IVF women more fertile in lighter months
31st March 2004
Researchers have found that pregnancy from IVF is more likely between
May and September, probably due to biological programming that we
have inherited from our primate origins.
The British Fertility Society hear today how investigators from
IVF clinics in Liverpool and Chester discovered that not only were
significantly less drugs required to stimulate ovulation in women
during the months with most daylight, but the implantation and successful
pregnancy rates were also markedly increased in months with longer
daylight hours.
Although historical records show that natural birth rates show
seasonal trends, conflicting evidence existed on the seasonal variability
of IVF. Now, UK researchers have carried out analysis on nearly
3000 standardised procedures that took place over a three-year period.
Trends seen between commonly defined seasons were not significant
but when they analysed results from the months with most daylight
hours (May-September) against those with least (November-February),
they found striking differences.
The amount of gonadotrophins (hormones used to stimulate the ovary
to produce eggs) required for ovulation was greater during the darker
days. The eggs harvested at different times of the year did not
vary in quality; fertilisation rates were unchanged. However, implantation
of the embryo into the uterus and completion of successful pregnancy
was significantly higher during the months with most daylight -
20% compared to 16%.
Local effects of the hormone melatonin may therefore be responsible.
Melatonin levels naturally cycle in response to light and dark,
and all mammals have physical responses to this cycling - the most
obvious being the natural sleep/wake patterns. Until recently it
was thought that melatonin acted only through the pituitary gland
in the brain. This natural system is purposefully switched off in
women who are undergoing fertility treatment, so it seems that melatonin
acts directly on the tissues of the female reproductive system to
make it more fertile in lighter months.
Dr Simon Wood, who carried out much of the study, commented ‘Although
we may not think that our bodies function differently from month
to month, our work indicates that human fertility is still influenced
by these primitive mechanisms common to all mammals.’
Notes for Editors
1Seasonality and the role of sunlight in Assisted Conception
cycles is presented at The Annual British Fertility Society Meeting
2004, in Cheltenham, UK
2SJ Wood*,#,##, A Quinn#,##, CR Kingsland# and Dr Lewis-Jones#,##
from *Dept Obs & Gyn, Countess of Chester Hospital, Chester,
#Hewitt Centre for Reproduction, Liverpool Womens Hospital, Liverpool
and ##Dept of Obs & Gyn, University of Liverpool, Liverpool,
UK
For more information: please contact the British Fertility Society press office
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