Influences Of Seasonal Variability And Meteorological Factors On The Outcome Of In Vitro Fertilization-embryo Transfer (ivf-et)

Background and objective:Epidemiologists throughout the world have consistently demonstrated a seasonal distribution in human natural conception and birth rates.Recent evidence suggests that deterioration in sperm quality during the hot summer in sub-equatorial areas,may result in lower conception rate leading to a reduction in the birth rate in spring.In northern countries,however,in regions where a strong seasonal contrast in luminosity exists,activity of the anterior pituary-ovarian axis and the conception rate are decreased during the dark winter months.In these areas,inversely,a peak in conception rate during summer leading to a maximum in birth rate in spring has been observed.Is such seasonal variability referred to human assisted reproduction technology?Many specialists in assisted reproduction technology units worldwide adhere to the notion that prenancy rate fluctuate throughout the year,the variation of prenancy rate is difficult to explain merely by technology and cultural conditions in laboratory. As outcome of in vitro fertilization-embryo transfer(IVF-ET) improves,correlating factors other than laboratory procedures have been investigated.Scientists and epidemiologists have previously reported various IVF outcomes in correlation with or without seasonal and weather influences.Different geographical areas with different weather may cause disparity in the results of IVF outcome.Better fertilization rates, embryo quality and pregnancy rates during the cold months have been observed,.other authers do not think so.So far there is not domestic information on the correlation of the fluctuation in prenancy rates associated with fertility treatments and seasonal variability.There is a little information in the literature abroad,and the few studies conducts so far have mostly been small,and the results are imcompatible because of the difference in the stimulation protocols used and the widely diverse environments with different climates.The research on the correlation of season and meteorological factors and the outcome of IVF is significance to clinical diagnosis and treatment.IVF-ET provides relatively unique controlled conditions for the study of seasonal influences on the human reproductive process.Thus,we have retrospectively evaluated our IVF population over a 4-year period to elucidate whether seasonality affects the human in vitro reproductive process.This study was designed to evaluate the effects of seasonality and meteorological factors on fertilization rate,cleavage rate, good embryo rate,implantation rate and pregnancy rate of IVF.Methods:All patients who received embryo transfer finally undergoing 1679 IVF-ET cycles of treatment are recruited from the Reproductive Center of The First Affiliated Hospital of Zhengzhou University from January 2004 to December 2007.A retrospective observational cohort study.A review of all individuals who received embryo transfer undergoing IVF-ET.Seasonal variability in fertilization rate,cleavage rate,good quality embryo rates,implantation rate and pregnancy rate of IVF and the correlation with the influence of air temperature,humidity,air pressure,the absolute number of light hours other environmental parameters.The methods of IVF-ET referred the routine ways of our center.We used SPSS software for the statistical analysis.The methods include:chi square test,partition of chi-square,multiple linear regression and logistic regression.Results:1.The fertilization rate negatively correlates with relative humidity,and the fertilization rate increases with lasting length of day.2.The cleavage rate changes with season,and is the lowest point in summer. When the air temperature increases and air pressure decreases,the cleavage rate is worse.The cleavage rate negatively correlates with cloud cover.3.The good quality embryo rate is the best in winter,and the worst in spring. The good quality embryo rate decreases in the high temperature weather.4.The implantation rate and pregnancy rate negatively correlates with ages of patients,and the pregnancy rate rises with light hours increasing.5.Seasonality seems to have significant influence on the quality of the human embryos possibly because of the temperature variations overtime.The pregnancy rate doesn't change with seasonal variability,and ages of patients is the important factor to determine the pregnancy rate of IVF-ET.Conclusions:Seasonality seems to have significant influence on the quality of the human embryos because of the temperature variations,but seasonality doesn't influence pregnancy rate finally.If this finding is confirmed,these seasonal changes should be taken into account when evaluating infertility data and in everyday clinical practice.