Caffeine addicts on fertility treatments may want to stop mainlining espresso while they're trying to have a baby. New data shows that women who drink five or more cups of coffee per day are severely reducing their chance of success with in vitro fertilization.

Danish scientists presented the study at the annual meeting of the European Society of Human Reproduction and Embryology. The study has not yet been published in a peer-reviewed journal.

The researchers followed up on nearly 4,000 women that were receiving IVF treatment at a large public clinic and found that the pregnancy rate fell 50%, and the live birth rate declined 40% among women that drank five or more cups of coffee a day.

Although we were not surprised that coffee consumption appears to affect pregnancy rates in IVF, we were surprised at the magnitude of the effect, said Ulrik Kesmodel of the Fertility Clinic of Aarhus University Hospital in Denmark, an author of the study.

Previous studies have made something of a link between coffee consumption and reproductive failure for women undergoing fertility treatment, though not as strong as the results seen here.

A 2002 study from UC San Diego scientists published in the journal Human Reproduction that examined 221 couples undergoing fertility treatment in Southern California found no significant effect of caffeine consumption on a woman's ability to get pregnant with IVF, but it did find that drinking even a moderate amount of caffeine (more than 2 milligrams per day) was a strong risk factor for miscarriage among the study's population.

The UC San Diego researchers also found that significant caffeine consumption meant that they tended to give birth more than three weeks earlier than women that consumed less than 2 milligrams of caffeine per day.

A 2010 study from Saudi Arabian researchers published in the journal Medical Science Monitor also found no association between coffee or tea consumption and the ability for women undergoing IVF to get pregnant. The researchers did find an association between heavy coffee drinking and miscarriages.

Given the limited and somewhat conflicting information on caffeine's effects on IVF treatment in the literature, Kesmodel says he would not wish to make patients worry 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, Kesmodel said in a statement Tuesday.