Seasonal changes may affect the pregnancy rate and other factors of assisted reproduction, according to a new meta-analysis of studies.
Outcomes are apparently better in the more temperate seasons of autumn and spring, suggesting that weather extremes may affect the process, either directly or indirectly, the study found.
"For patients and physicians hailing from tropical countries, IVF results will be affected in the summer, but if they hail from temperate or cold countries, results are a touch better in summer than in winters," Dr Srisailesh Vitthala, who led the study at the Kamineni Fertility Center in Hyderabad, India, told Reuters Health by email.
Dr Vitthala presented results from the new analysis at the American Society for Reproductive Medicine annual meeting in San Diego.
How the study was done
The researchers analysed results from 10 studies on in vitro fertilisation and intracytoplasmic sperm injection outcomes according to the seasons.
They found the lowest clinical pregnancy rates in the summer, 18%, and the winter, 21%, and the highest in the spring, 27%, and autumn at 24%.
Fertilisation rates were similar across the seasons at a low of 43% in the winter up to a high of 46% in the autumn.
The number of oocytes retrieved was lowest in the winter at 22% and summer, at 23%, climbing to 29% in the autumn and 27% in the spring.
Humidity and pollution in the summer could affect fertilisation, Dr Vitthala said, as could the lack of sunlight in the winter in colder regions.
But indirect consequences of extreme weather might have a stronger impact, including interrupted power supplies and refrigeration problems for hormone medications, according to Dr Vitthala.
The results warrant larger studies in different continents to test the findings, Dr Vitthala said.
A few such studies have already been done, and the findings don't agree with Dr Vitthala's.
In 2011 investigators from Croatia analysed the influence of seasonal variations on the number of retrieved ova, fertilisation rate, embryo quality rates and pregnancy rate in 2 140 IVF cycles and found no impact of seasonal changes. That study was published in a journal called Collegium Antropologicum.
And in 2005, researchers at the University of Turin reported in Gynecological Endocrinology that based on findings in 2 067 patients, "the results of a good-quality IVF program in humans are not significantly affected by the season of the year in which the IVF attempt is accomplished."
Still, there doesn't appear to have been much work on the topic. The vast majority of studies looking at seasonal impacts on IVF results have been done in animals, not humans.
(Reuters Health, October 2012)
5 million fertility babies born since the first
IVF may raise birth defects risk
IVF in young women tied to breast cancer