Summary
Objective. The aim of this study was to investigate the impact of seasonality and weather conditions on zona pellucida (ZP) thickness and assisted reproductive treatment (ART) outcome.
Materials and methods. 959 in vitro Fertilization (IVF) and Intra cytoplasmic Sperm Injection (ICSI) cycles conducted in Santaros Fertility Center, Lithuania during 2017–2019 were retrospectively analyzed. The sperm concentration, number of retrieved and fertilized oocytes, transferred embryos, fertilization and pregnancy rates were compared among four seasonal groups – winter, spring, summer, autumn. Later only IVF cycles were analyzed. The ZP thickness was measured of 5001 oocytes. It was evaluated if seasonality, ambient temperature, precipitation, sunshine and lunar phase influence ZP thickness.
Results. In IVF/ICSI group the sperm concentration was highest in the winter (89.00±57.35×106/ml) and lowest in the summer (72.13±58.42×106/ml) (p=0.009) and the odds were 1.49 times higher to conceive in spring compared to summer (95% CI 1.01–2.21; p=0.046). The ZP thickness was highest in autumn (19.42±2.98 mm) and lowest in summer (18.81±2.65 mm) (p<0.05). The thickness was also highest during the new moon phase, when the average monthly temperature was 2.8–8.5 °C, when total monthly precipitation was more than 80 mm and when total monthly sunshine time were less than 30 hours (p<0.05). The ZP thickness was lowest during the last quarter moon phase, when temperature was lower than 2.8 °C, when precipitation was 30–60 mm and when there was sunshine for 155–242 hours per month (p<0.05).
Conclusion. Seasonality and weather conditions impact zona pellucida thickness and ART outcome.
