P–729 Seasonality and lunar phase impact zona pellucida thickness while assisted reproductive treatment outcome shown no differences between seasons
Authors: Gudleviciute A , Maldunas P , Gersvaltaityte G , Gudlevicien Z , Paliulyt V 
Published: August 2021

Study question

Does seasonal variation impact zona pellucida (ZP) thickness, other assisted reproductive treatment (ART) factors and ART outcome?

Summary answer

Seasonality and lunar phase impact ZP thickness while specific weather conditions alone do not, however, seasonality does not impact other ART factors or ART outcome. What is known already: Several epidemiological studies have demonstrated seasonal variation in natural pregnancy and birth rate, which varies across geographic regions. It has been suggested that temperature and light may affect the ability to conception via hormonal changes. However, data regarding the seasonal variation during ART is controversial and several studies with conflicting results have been published. One retrospective observational cohort study reported the significant influence of seasonality on fertilization rates with highest ones during the spring and the lowest ones in the autumn. However, another retrospective study did not demonstrate any significant influence of the seasons on ART outcome.

Study design, size, duration

This retrospective study was performed in the Fertility Center, VUH Santaros Clinics, Lithuania. 959 IVF/ICSI cycles conducted in IVF laboratory between 2017 and 2019 were analysed. The thickness of ZP was measured of 5002 oocytes retrieved between 2017 and 2018. Degenerated oocytes were excluded from the study. Average temperature (AT), precipitation (AP) and sunshine hours (ASH) of every month were taken from Lithuanian Hydrometeorological Service database. Lunar phase (LP) data was collected using Google Calendar.

Participants/materials, setting, methods

IVF/ICSI cycles were divided into four seasonal groups according to the day of oocyte pick-up. The number of retrieved and fertilized oocytes, transferred embryos, fertilization and pregnancy rates were compared among groups. Then, to avoid bias in fertilization rate, ICSI cycles were excluded and only IVF cycles were analysed. Measurements of ZP thickness were taken using NIS-Elements F software. It was evaluated if AT, AP, ASH, LP and seasonality had an effect on ZP thickness.

Main results and the role of chance

The mean number of retrieved oocytes and fertilized oocytes as well as the percentage of women who conceived was highest in the spring and lowest in the summer without statistical significance among all seasonal groups (p &gt; 0.05). The fertilization rate was lowest in the spring (66.60%) and highest in the autumn (68.76%) without statistical significance among all four groups. The odds were 1.49 times higher to conceive in spring compared to summer and this result was statistically significant (95% CI 1.01–2.21; p = 0.046), however, when comparing all four seasons together, the difference was not significant. The calculations with only IVF cycles followed the same pattern except that the odds ratio results were not significant and the fertilization rate was highest in the winter. None of the weather conditions (average temperature, average precipitation and average sunshine hours) had an impact on ZP thickness. However, the mean ZP thickness was lowest in the summer (18.86 ± 3.08 µm) and highest in the autumn (19.43 ± 2.98 µm) and the difference among all four seasons was statistically significant (p &lt; 0.05). The mean ZP thickness was lowest during the first quarter lunar phase and highest during the new moon phase with statistical significance among groups (p &lt; 0.05).

Limitations, reasons for caution

A limitation of our study is unequal number of the IVF/ICSI procedures between months/seasons (e.g., the sample size of autumn was 340 while the sample size of summer was only 161). Also, the measurements of ZP were taken manually therefore there could be some errors.

Wider implications of the findings: Understanding possible effects of external factors on ART outcome is important for the best treatment results. Even though seasonality and lunar phase significantly impact ZP thickness, we could not demonstrate any significant seasonal influence on other ART factors or ART outcome. Further studies with higher number of patients are required.

Trial registration number

Not applicable