Higher fertilisation rates have been found in women undergoing IVF in spring, according to new research presented at the World Congress of Fertility and Sterility last week.

The study analysed 1932 patients undergoing ICSI (intracytoplasmic sperm injection) - 435 patients in winter, 444 in spring, 469 in summer and 584 in autumn. While the percentage of developing eggs, high-quality embryos, implantation, and pregnancy rates did not differ among the group, the fertilisation rate was significantly higher during the spring.

Those who had treatment in March, April or May were 1.5 times more likely to conceive than at any other time of the year. The success rates were: 67.9 per cent in winter, 73.5 per cent in spring, 68.7 per cent in summer and 69 per cent in autumn. All the patients in the study came from one clinic - Sao Paulo's Assisted Fertilisation Center.

Dr Daniela Braga, head researcher at the centre and leader of the study, said: 'This work shows that IVF cycles may have a better outcome during the spring. 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'.

Dr Braga believes the increase in light in spring could trigger women's bodies to produce higher levels of estradiol, a hormone important for fertilisation of the egg and development of the embryo. Through blood samples taken from the participants in the study, higher levels of estradiol were detected in spring.

But experts say the findings do not suggest women should wait until the spring to undergo fertility treatment, as this may be risky. Dr David Keefe, Chair of Obstetrics and Gynaecology at the NYU Langone Medical Centre in New York City, said: 'First, when we do in vitro, we're already overriding the whole system and the hormones that turn on reproduction'.

'And, second, species that have a longer gestation, such as humans, have typically bred when the days are getting shorter, and they [the study authors] found the opposite here', he added. 'In addition, humans aren't as controlled or hardwired to environmental changes any more. We live in artificial lights, and control the temperature and humidity, so many cues that would trigger breeding, we control all the time. We've insulated ourselves against environmental changes'.

Dr Braga highlighted the success of IVF, no matter what the season: 'Despite the better results obtained in spring, it is important to highlight that assisted reproduction techniques are effective regardless of the season in which the treatment is being performed', she said.

The Daily Mail reports the study supports findings from previous research at the Countess of Chester Hospital and Liverpool Women's Hospital, which found 20 per cent of IVF cycles from May to September resulted in a successful pregnancy, compared to 16 per cent for the remainder of the year.

The study was initially reported in a press release from the World Congress of Fertility and Sterility. BioNews asked John Parsons, a Progress Educational Trust trustee and retired gynaecologist, to comment on the study, using information given in the press release.

He said about the release: 'The study appears to be a retrospective analysis of data. It is not clear over what time period [the research was done], but I suspect over a single year, or whether there was more than one clinic involved'. Using information in the release alone, he felt unable to comment upon or draw any conclusions from the study.