Coffee and cake lowers IVF success
Regular trips to the coffee machine or having a diet packed with saturated fat have been linked to lower IVF success rates by fertility experts.
One study suggested heavy coffee drinking was as bad as smoking for IVF success rates.
Another showed saturated fats lowered the number of eggs that could be used in IVF, while a 'Mediterranean diet' boosted birth rates.
Experts say lifestyle affects both the chances of IVF and natural conception.
Dr Ulrik Kesmodel, a consultant gynaecologist, presented data at the European Society for Human Reproduction and Embryology (ESHRE) meeting in Turkey.
It involved 3,959 women having IVF at the Aarhus University Hospital in Denmark.
One in 20 women were drinking more than five cups of coffee a day. This group of women were half as likely to become pregnant as those who did not drink coffee.
The researchers said this was as damaging to the chances of a successful pregnancy as smoking.
Dr Kesmodel said: "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."
It is not known whether drinking tea or other caffeinated drinks would have the same effect.
Dr Kesmodel said: "The assumption is that caffeine is the culprit although we don't really know. There are so many substances within coffee."
The British Coffee Association said a there was no need to completely cut caffeine from the diet as there were "no harmful effects" with low levels of consumption.
Its executive director, Dr Euan Paul, said: "For pregnant women or those trying to conceive, an upper limit of 200mg of caffeine per day is perfectly safe.
"This is the equivalent of 2 to 3 cups of coffee."
A separate analysis by the Harvard School of Public Health, in the US, investigated how differences in 147 women's diets affected IVF.
Diets high in saturated fats, such as those from butter, fatty meats and cheese, lowered the number of eggs a women produced for IVF.
Meanwhile a diet high in unsaturated fats, such as olive oil and avocados, was associated with an increase in the live birth rate, although there were too few women in the study to say exactly how big the increase was.
The lead researcher Dr Jorge Chavarro said that women should consider adapting their diet anyway as it is already considered to be good for cardiovascular disease and Type 2 diabetes.
He said: "We know that these types of diets are generally healthy and from that perspective I think it makes total sense not only for women undergoing assisted reproduction, but anyone, to follow these kinds of diets."
Richard Kennedy, the secretary of the International Federation of Fertility Societies, said that "many" lifestyle choices made it harder to conceive both naturally and through IVF.
He said: "This work reinforces the need for a good lifestyle for those trying to have a baby; eat and drink in moderation, and don't smoke."