Drinking more than five cups of coffee a day or having a diet with too much saturated fat could adversely affect the chances of success of fertility treatment.
These are the conclusions of two separate - and as yet unpublished - studies presented at the annual meeting of the European Society of Human Reproduction and Embryology in Istanbul, Turkey.
Dr Ulrik Kesmodel, a gynaecologist at the Aarhus University Hospital Fertility Clinic in Denmark presented a follow-up study on 3,959 women who had IVF or ICSI. One in 20 patients reported drinking more than five cups of coffee a day at the start of their treatment.
These women were half as likely to become pregnant as those who did not drink coffee and their chance of a live birth was reduced by 40 percent, although this latter trend was not statistically significant.
No significant effect was observed for patients drinking less than five cups per day. The study's authors conclude that if their research is accurate, the effect of consuming five cups or more of coffee a day would be comparable to the detrimental effect of smoking on reducing clinical pregnancy.
Dr Kesmodel said: 'There is limited evidence about coffee in the literature, so we would not wish to worry IVF patients unnecessarily. But it does seem reasonable, based on our results and the evidence we have about coffee consumption during pregnancy, that women should not drink more than five cups of coffee a day when having IVF'.
The study specifically investigated the effect of coffee consumption, rather than looking at all caffeinated beverages. Dr Kesmodel said that, as a result, 'the assumption is that caffeine is the culprit although we don't really know. There are so many substances within coffee'.
BBC News reported the response of the British Coffee Association's executive director, Dr Euan Paul. He said: 'For pregnant women or those trying to conceive, an upper limit of 200 milligrams of caffeine per day is perfectly safe. This is the equivalent of 2 to 3 cups of coffee'.
A second study, presented by Dr Jorge Chavarro, assistant professor of nutrition from the Harvard School of Public Health in the USA, looked at the relation between dietary fat intake and treatment outcomes for 147 IVF patients.
The study found that women who had more saturated fats in their diet, such as those found in butter and meat, had fewer eggs available for collection during IVF.
Conversely, greater consumption of monounsaturated fats, such as those found in olive oil and avocados, was associated with an increase in live birth rate. However, there were too few women in the study for researchers to measure how important this effect was.
Dr Chavarro admitted that the findings were tentative: 'This is the first time to our knowledge that dietary fats have been linked to treatment outcome in IVF. So it is important that our results are replicated in other studies before making strong recommendations about fat intake to women having infertility treatment'.