IVF may be more successful if eggs are collected in the summer

A new study by Australian researchers suggests that the timing of egg retrieval from a woman’s ovaries during fertility treatment appears to influence fertility.The research results were published in a journal human reproductionThey found that implanting frozen and thawed embryos from summer eggs into a woman’s uterus was 30 percent more likely to give birth to a live baby than if the eggs were harvested in the fall.

To date, there have been conflicting findings about the effects of season on pregnancy and fertility after egg retrieval and embryo freezing. As study leader Dr. Sebastian Leatheric explained, King Edward Memorial Hospital, City Fertility Australia and Fertility specialist in Western Australia“It has long been known that there are seasonal variations in natural fertility rates around the world, but many factors, including environmental, behavioral and sociological factors, may contribute to this.

“Most of the studies looking at the success rate of in vitro fertilization have focused on fresh embryo transfers in which the embryos are returned within a week after egg retrieval. Potential effects on implantation and early gestational development cannot be isolated.

“Recently, many embryos are frozen and transferred at a later date. We thought it would give us an opportunity to investigate separately.”

Leathersich et al. analyzed the results of all frozen embryo transfers performed at a single clinic in Perth over eight years from January 2013 to December 2021. During this period, 3659 frozen embryo transfers were performed and embryos were produced in 2155 IVF cycles. to 1835 patients. Two frozen embryo transfers were excluded due to lack of information on outcome, and 3657 were included in the analysis.

The researchers used meteorological data obtained from the Bureau of Meteorology to examine birth outcomes according to season, temperature, and actual hours of daylight (rather than calculating the time from sunrise to sunset). The researchers compared the number of hours of sunshine on the day the eggs were collected, with low sunshine (0-7.6 hours), medium sunshine (7.7-10.6 hours), and high sunshine (10.7 hours). ~13.3 hours) were created into three groups.

“When we looked specifically at the sunshine hours during the egg-laying season, we saw a similar increase to the summer egg-laying,” Leathersick said. “The live birth rate after frozen embryo transfer from oocytes collected on days with low sunshine was 25.8%. This rate increased to 30.4% when embryos were born from oocytes collected on days with maximum sunshine. This improvement was still seen, even taking into account the season and conditions on the day of embryo transfer.”

The temperature on the day of egg retrieval did not affect the chance of littering. However, embryos transferred on the hottest day (mean temperature 14.5-27.8°C) had an 18% lower, slightly increased chance of live birth compared to the coldest day (0.1-9.8°C). . The miscarriage rate went from 5.5% to 7.6%.

“Our study suggests that optimal conditions for birth appear to be associated with increased daylight hours in the summer and on egg retrieval days,” Leathersick said.

“In our study, the overall live birth rate after frozen embryo transfer was 28 per 100 live births. There were 31 live births per 100. This improved birth rate was seen regardless of when the embryos were finally implanted in the woman’s uterus: birth rates were higher when eggs were collected in spring or winter. , was between these two numbers.”

Factors that may be responsible for increased fertility after egg retrieval during summer and long periods of sunshine include melatonin. Levels of this hormone are usually higher in winter and spring, and it takes three to six months for the egg to develop and be released from the ovary. Differences in lifestyle between winter and summer may also play a role.

The findings that miscarriage rates were highest when embryo transfers occurred on the hottest day are consistent with epidemiologic studies showing higher miscarriage rates in the summer. “This suggests that the adverse effects of high temperatures are more likely to be related to early pregnancy than egg development,” says Leathersich.

Leathersick acknowledged that there are many factors that influence fertility success, including age, smoking, avoidance of alcohol and other toxins, and maintaining a healthy activity level and weight. But the study suggests that clinicians and patients can also consider the importance of environmental factors and their effects on egg quality and embryonic development, he said.

“We have effectively separated the conditions at the time of oocyte retrieval from the conditions at the time of implantation, demonstrating that environmental factors during oocyte development are as important or even more important than those during implantation and early pregnancy. I did,” he said. .

Leathersich also said that because the study was a retrospective rather than prospective study, it could not show that conditions at the time of egg retrieval caused differences in fertility rates, only that they were associated with them. rice field. Ideally, the study should be replicated at other centers with different conditions and different treatment protocols, he said, to confirm the findings.

“It would also be interesting to examine the effects of seasonal and environmental factors on sperm parameters, as this may have contributed to our observations,” he said. “We currently plan to analyze this same group of patients using air quality data because exposure to harmful pollutants has seasonal variations and can adversely affect reproductive outcomes. I’m here.

“Finally, given the significant increase in so-called ‘social egg freezing’ for fertility preservation and the fact that this group is generally flexible about when to receive treatment, these It will be very interesting to see if the observations of ‘ also hold true for frozen oocytes’ thawed and fertilized eggs years later. Improved results in this group could have a significant impact on women making future fertility decisions, but long-term follow-up is needed before any conclusions can be drawn about this population. can take a while. ”

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