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IVF success may depend on what season eggs are collected, study finds – National | Globalnews.ca

Collecting human eggs for fertility treatment may create more favourable results when performed during the sunny summer season compared to a cloudy fall day, according to new research.

The Australian study, published Wednesday in Human Reproduction, looked at outcomes from frozen embryo transfers over an eight-year period and discovered that the time of year when eggs are collected from a person’s ovaries during fertility treatment may be impacted by the season and duration of sunshine.

“What we found is that the time (of the year) you put the embryo back didn’t actually seem to have any impact on the live birth rate,” Dr. Sebastian Leathersich, an obstetrician and gynecologist based in Perth, Australia, and lead author of the study told Global News.

Instead, the researchers found that if the egg had been collected in summer as opposed to the fall, the odds of having a successful embryo transfer and live birth were 30 per cent higher regardless of when the embryo was implanted in the womb.

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In vitro fertilization (IVF) is one of the most expensive fertility treatments but the most successful, according to IVF Canada. The process involves removing eggs from ovaries and fertilizing them with sperm in a laboratory before being implanted in the womb.

According to Dr. Evan Taerk, a specialist in reproductive endocrinology and infertility based in Toronto, the methods of performing IVF in Australia are largely comparable to those in Canada.

“Although it’s not a complete uniformity, there are a lot of similarities between a cycle (done) in Australia and when you would do, let’s say in Montreal or Toronto or Winnipeg,” he explained.

During IVF, Leathersich said most clinics will flash freeze the embryo (a fertilized egg) in order to preserve it, meaning a lot of embryos are placed back in the womb having been frozen for months or even years.

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Live birth rates are a measure of a fertility treatment’s (like IVF) effectiveness in achieving a live-born baby.

In order to see if environmental factors contribute to live birth rates, the researchers looked at outcomes from all frozen embryo transfers carried out at a single clinic in Perth from January 2013 to December 2021. During this time, there were more than 3,600 frozen embryo transfers with embryos generated from 2,155 IVF cycles in 1,835 patients.

They also examined birth outcomes according to season, temperatures and the actual number of hours of bright sunshine.

The overall live birth rate following frozen embryo transfer was 28 births per 100 people. If eggs were collected in autumn, it was 26 births per 100 people, but if they were collected in summer there were 31 births per 100 people.


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The researchers also found a 28 per cent increase in the chances of a live birth among women who had eggs collected during days that had the most sunshine compared to days with the least sunshine.

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The temperature on the day of egg collection did not affect the chances of successful fertility treatment, the study found. However, the chances of live birth rate decreased by 18 per cent when the embryos were transferred on the hottest days (average temperature of 14.5-27.8 C) compared to the coolest days (0.1-9.8 C).

This is not the only study to find these results.

A 2021 study out of Boston, Mass., yielded similar findings. The researchers found that eggs collected during summer had a higher live birth rate compared to eggs collected in other seasons.

But unlike the study out of Perth, the researchers found that winter had the lowest success rates instead of the fall.

What are the reasons behind the findings?

Although the Perth study found that summer may make a difference when eggs are retrieved from an ovary, the reason why is still not known, Leathersich said.

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But there are theories, and one of them includes melatonin — the sleep hormone that helps with circadian rhythm and also has antioxidant qualities.

“What we know is that the levels of melatonin are much higher during winter,” he said. “And we also know that egg development takes at least three months, but probably somewhere closer to nine months before that egg is actually released.”

It’s possible that melatonin exposure in the three to nine months before removal (which land in the winter or early spring), may actually impact the development competence of the egg, he explained.

“And of course, this does require a lot more research and it would be really good to see these sorts of studies replicated in different centers around the world where potentially there’s different environmental factors and different patient factors,” he added.

Differences in lifestyles between winter and summer months may also play a role, he said.

While recognizing the significance of studies like the one conducted in Perth, Taerk noted it’s not without limitations.

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“When we say there’s an association between summer and an increased rate of live birth rate, is it the sunshine that’s doing it? Is it other behavioural factors such as diet, lifestyle, the air quality?” he questioned.

Dr. Taerk also noted the study lacked sperm-related information, which could potentially contribute to the success of IVF treatment.

“Could these same seasonal effects that may be impacting the eggs also be affecting the male factor side?” he asked.

Given the limitations of the study, he said it’s important for people considering IVF that delaying the procedure for a different season may come with risks.

“The more time that’s delayed the potential impact that can have on the number of eggs retrieved and ultimately IVF outcome,” he said. “And I’m not sure we can say at this point that it’s going to be beneficial to wait until a specific season to do that.”


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Leathersich and Taerk both agree that more studies need to be conducted in order to further understand and validate the findings.

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“I don’t think people should be rushing out and canceling winter IVF cycles,” Leathersich said. “But really what this does is show the important role that environment plays in egg development and reproductive outcomes.

“And there are many factors that affect activity in the success of fertility treatment, chief among them really being both maternal age and paternal age.”

He added that there are several factors within people’s control that can positively influence fertility outcomes. These include avoiding smoking, minimizing alcohol consumption, limiting caffeine intake and maintaining a healthy balanced diet.

“We know that IVF treatment is a big burden to patients: a physical burden, a medical burden, psychological burden, and a financial burden,” Leathersich said.

“So ongoing research that can reduce the burden of treatment and increase the success of treatment is vital.”



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