Brazilian scientists have discovered that the success of in vitro fertilization (IVF) depends on the season of the year in which the egg is released, reports ScienceDaily. Researchers from the Center for Assisted Reproduction in São Paulo analyzed the cytological and biochemical parameters of eggs taken from 1,932 patients with reproductive problems undergoing ICSI fertilization. The ICSI method is similar to the IVF method, but in it a sperm is injected into the ovum using a special technique. In 435 of the women (22.5%), the manipulation was performed in winter, 444 (23%) – in spring, 469 (24, 2%) – in summer and 584 (30.3%) – in autumn. It was found that the percentage of fertilized eggs, the resulting embryos suitable for implantation, their implantation in the uterus and the occurrence of pregnancy differed between the individual groups of participants in the study. It turned out that the frequency of successfully fertilized eggs was significantly higher in the spring (73.5%) compared to the winter season (67.9%). In summer and autumn, the percentage of successful fertilizations was 68.7 and 69 percent, respectively. The analysis of the obtained data shows that the chance of successful fertilization of eggs released in the spring is 1.45 higher than in the other seasons. According to the head of the research Daniela Braga, the observed dependence can be attributed to the influence of the level of natural lighting to produce gonadotropin-releasing hormone from the hypothalamus, which controls the production of sex hormones. This is supported by the fact that higher levels of 17-β-estradiol (the main estrogen) were reported in spring than in any other season. The authors of the study advise women, especially those who have had an unsuccessful IVF experience in the past, to prefer spring as the season in which to perform artificial insemination.