A NEW retrospective cohort study from Jinan, China suggests that seasonal environmental factors may meaningfully influence IVF outcomes, with spring cycles showing higher full-term and live birth rates than winter, but also an increased risk of early miscarriage. The findings add to growing evidence that temperature, light exposure and seasonal hormonal rhythms may shape reproductive physiology.
Spring Shows Divergent IVF Outcomes
Researchers analysed 2,551 first fresh IVF cycles performed between 2009 and 2024 in women under the age of 35 with normal ovulation and no major uterine or severe male-factor infertility. Outcomes were compared across four seasonal groups based on stimulation start date. While clinical pregnancy rates did not differ significantly by season, spring cycles demonstrated consistently better downstream outcomes.
Weighted analyses revealed significantly higher live birth rates and full-term delivery rates in spring compared with winter. However, the spring cohort also experienced a 70% increase in miscarriage risk, indicating a complex physiological pattern: early vulnerability followed by stronger developmental progression among ongoing pregnancies.
Sunlight on Trigger Day May Influence Success
A secondary analysis of meteorological variables found that higher sunlight intensity on the trigger day was associated with lower pregnancy success (OR 0.978 per lux-unit increase). The authors propose that altered circadian signalling and melatonin suppression could impair implantation or early embryo support.
Implications for Practice
Although environmental exposures did not eliminate the role of established predictors, such as embryo quality, endometrial thickness and ovarian reserve, the findings suggest that seasonal microenvironments could influence IVF trajectories, particularly in regions with marked climatic variation. The authors call for prospective studies integrating temperature, circadian biomarkers and hormonal profiling to determine whether seasonally informed protocol timing may optimise outcomes.
Reference
Hu X et al. The impact of seasonal variations on IVF pregnancy outcomes: a retrospective cohort study in Jinan, China. Front Med. 2025;12:1681770.
