In Vitro Fertilization Works Better in the Spring, Study Suggests
In the spring, they say, a young man's fancy lightly turns to thoughts of love. That might have something to do with the fact that it's easier for a woman to conceive in the spring than during any other season.
According to a study presented Sept. 14 at the World Congress of Fertility and Sterility in Munich, Germany, in vitro fertilization rates were found to be highest in the spring (73.5 percent) versus the winter (67.9 percent), summer (68.7 percent) or fall (69 percent).
Scientists have long noted seasonal variations in the number of births resulting from natural conception. Although there has been no firm explanation for this trend, it is believed that human reproduction is linked to temperature and season, according to researchers.
This new study suggests even assisted reproduction may be more effective during certain times of the year.
The researchers, led by Dr. Daniela Braga of Sao Paolo, Brazil, examined the biological characteristics of 1,932 patients undergoing egg retrieval for intracytoplasmic sperm injection (ICSI) -- a type of assisted reproduction used to treat sperm-related infertility -- during the different seasons of the year.
The results showed there was no difference in the percentage of developing eggs, high-quality embryos, implantation and pregnancy rates between the winter, spring, summer and autumn groups.
However, the fertilization rate was significantly higher during the spring (73.5 percent) than during any other season -- in fact, it was found to be almost one-and-a-half times that of other seasons, according to the study.
"This work shows that IVF cycles may have a better outcome during the spring," Braga says in a press release. "In practical terms this may mean that if you are having real difficulty in conceiving, it may be better to have an assisted reproduction cycle during this season."
The study also found that levels of 17-β estradiol -- the main estrogen hormone found in women between puberty and menopause -- were significantly higher in the spring. The authors suggest this may be due to the effect of changing light on brain mechanisms which affect the secretion of estradiol from the ovaries.
"In assisted reproduction, adequate estradiol levels are important for egg maturation and other reproductive processes including fertilization and embryo development," Braga reports.
However, not everyone is convinced that seasonal differences are a factor in in vitro fertilization. Dr. David Keefe, chairman of obstetrics and gynecology at the NYU Langone Medical Center in New York City, tells BusinessWeek that women might be risking their fertility even further if they try to wait for what might be perceived as a more fertile time of the year.
"First, when we do in vitro, we're already overriding the whole system and the hormones that turn on reproduction. And, second, species that have a longer gestation, such as humans, have typically bred when the days are getting shorter, and they (the study authors) found the opposite here," he says.
Keefe tells BusinessWeek humans aren't as controlled or hardwired to environmental changes any more.
"We live in artificial lights, and control the temperature and humidity," he says, "so many cues that would trigger breeding, we control all the time. We've insulated ourselves against environmental changes."
But what's important in this study for people considering IVF is that no differences were found between seasons in pregnancy rates, which is what really matters to those trying to conceive, the magazine reports. And the researchers seem to agree.
"Despite the better results obtained in spring, it is important to highlight that assisted reproduction techniques are effective regardless of the season in which the treatment is being performed," Braga says.
Related: In-Vitro Babies Show (Slightly) Higher Risk for Cancer
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