Women seeking to become pregnant may want to avoid coffee, according to a number of studies that linked delayed conception with drinking as little as 474 milliliters (about two cups) of coffee a day.

Researchers from the University of Nevada School of Medicine in Reno have now found that the smooth muscles of the Fallopian tubes are prevented from contracting by caffeine, making it difficult for the eggs to travel from the ovaries to the womb.

Describing the effects of coffee on the fallopian muscles as “profound,” the researchers said that the effects were noted after caffeine is ingested “in concentrations well within what people are drinking,” “Caffeine has been reported to be ‘the most frequently ingested pharmacologically active substance in the world,’ the researchers said in a report published in the British Journal of Pharmacology. 

“I would suggest that if women are trying to get pregnant, they lay off the coffee, and cola as well,” according to Sean Ward, a professor of physiology and cell biology who took part in the research. “The effects of caffeine on the oviduct can be quite sustained.”