Season and sunshine hour effects on live birth rates in IVF treatments

Woman in white clothes lying on the grass and looking at the sun

The timing of egg retrieval during fertility treatment may significantly impact live birth rates, according to recent research published in Human Reproduction, a prominent reproductive medicine journal. Australian researchers discovered that harvesting eggs during the summer months resulted in a 30% higher likelihood of live births when compared to egg retrieval in the autumn.

Dr. Sebastian Leathersich, an obstetrician, gynecologist, and Fellow in Reproductive Endocrinology and Infertility, led the study, highlighting that the overall live birth rate following frozen embryo transfer in Australia averaged 27 births per 100 people. However, when eggs were collected in the summer, the rate increased to 31 births per 100 people, as opposed to 26 births per 100 people for eggs collected in autumn. The live birth rates for spring and winter fell between these two figures and were not statistically significant.

Additionally, the researchers noted a 28% increase in the chances of a live birth for women whose eggs were collected on days with the most sunshine compared to those with the least sunshine.

Previous studies had conflicting findings on the impact of seasons on pregnancy and live birth rates, particularly in relation to egg collection and embryo freezing in IVF.

Dr. Leathersich explained that while seasonal variations in natural birth rates have long been recognized worldwide, these can be influenced by various factors, including environmental, behavioral, and sociological elements. Most studies on IVF success rates primarily focused on fresh embryo transfers, which made it challenging to separate the potential effects of environmental factors such as season and sunshine hours on egg development from those on embryo implantation and early pregnancy.

In contrast, many embryos are now frozen and transferred at a later date, providing an opportunity to explore the impact of the environment on egg development and early pregnancy separately. The researchers analyzed data from 3,657 frozen embryo transfers conducted at a single clinic in Perth over an eight-year period.

The study revealed that higher live birth rates were associated with summer egg collection and increased sunshine hours at the time of retrieval. Interestingly, the temperature on the day of egg collection did not affect live birth rates, but transferring embryos on the hottest days led to an 18% decrease in live birth rates and a slight increase in miscarriage rates.

Dr. Leathersich emphasized that while age remains a critical factor in fertility treatment success, this study underscores the significance of environmental factors in influencing egg quality and embryonic development. He suggested that clinicians and patients should consider external factors like environmental conditions alongside lifestyle choices to optimize fertility outcomes.

The research also raised questions about factors like melatonin levels and differences in lifestyle between seasons, which may contribute to the observed variations. Future studies are needed to confirm these findings in different settings and to explore the impact of season and environmental factors on sperm parameters. Additionally, the researchers plan to analyze air quality data to examine the effects of harmful pollutants on reproductive outcomes.