Scientists say that couples trying for babies with IVF are more likely to conceive in spring than at any other time of year.
Scientists discovered that those who had treatment in March, April or May were one-and-a-half times more likely to be successful than those trying during other months.
Experts believe that the increase in light in spring could trigger women's bodies to produce greater amounts of the sex hormone estradiol, crucial for the fertilisation of the egg and development of the embryo.
Scientists from the Assisted Fertilization Center in Sao Paulo, Brazil looked at almost 2,000 women undergoing IVF treatment during all four seasons of the year.
They found that rates of fertilisation - when the egg and sperm join together to make an embryo - and levels of estradiol in the women's blood were significantly higher in spring.
Dr Daniela Braga, who led the study presented to the World Congress on Fertility and Sterility in Munich, suggested that changing light levels caused neurons in women's brains to produce certain hormones, which in turn increased the amount of estradiol produced by the ovaries.
"This work shows that IVF cycles may have a better outcome during the spring," the Daily Mail quoted her as saying.
"Our results show a significant difference in spring fertilization rate, with the fertilization rate in the spring being almost one-and-a-half-times that of other seasons.
"In practical terms this may mean that if you are having real difficulty in conceiving, it may be better to have an assisted reproduction cycle during this season.
"We found higher estradiol levels in the spring. In assisted reproduction, adequate estradiol levels are important for egg maturation and other reproductive processes including fertilization and embryo development," she added.
The scientists now want to test if women are more likely to conceive in areas of Brazil nearer the equator, where there is more light.
The findings back up work carried out by British scientists that showed that fertility treatment was more likely to be successful in spring or summer.
A team from Countess of Chester Hospital and Liverpool Women's Hospital found that 20 per cent of IVF cycles from May to September resulted in a successful pregnancy, compared with 16 per cent for the remainder of the year.
The researchers suggested that this was down to humans showing the same biological processes as those that occur in birds and mammals.