New research indicates that couples undergoing in vitro fertilization (IVF) may see higher pregnancy success rates during warmer months, with summer emerging as the most favorable season.
Published in the International Journal of Biometeorology, the study analyzed data from 1,100 first-time IVF patients at the Reproductive Hospital of Guangxi in China between June 2021 and October 2023, all using fresh embryos rather than frozen ones.
The findings revealed striking seasonal differences: compared to colder months, pregnancy rates were 75% higher in spring and 53% higher in summer.
Notably, among patients following the “long protocol”—a standard IVF procedure in the UK that involves suppressing natural hormones before ovarian stimulation—summer success rates doubled.
Researchers highlighted that temperatures between 26–30°C (79–86°F) correlated with the highest pregnancy rates, suggesting that scheduling treatments within this temperature range could optimize outcomes.
They hypothesize that increased vitamin D levels, often called the “sunshine vitamin,” may play a key role. Produced by the body in response to sunlight, vitamin D is linked to hormonal balance and fertility, and the NHS advises UK residents to take supplements during winter due to reduced sunlight exposure.
While the exact mechanisms behind the seasonal variation remain unclear, the study aligns with previous research pointing to environmental factors influencing IVF success. The team noted that vitamin D deficiency is associated with chronic conditions like osteoporosis and heart disease, underscoring its broader health importance.
“Our findings suggest that season and temperature significantly influence clinical pregnancy success, with summer treatment potentially optimizing IVF outcomes,” the researchers concluded, calling for further studies to clarify vitamin D’s role in reproductive health.
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