Although there is no link to the original source of the study, ABCinfertility.com talks about how coffee significantly increases the risk of miscarriage:
Are you aware of the scientific fact that drinking coffee before and during pregnancy doubles the risk of miscarriage? Studies have found that drinking as little as one cup of coffee per day increase the risk of non conceiving by 55%. Every additional cup keeps raising the risk even further. There are great coffee substitutes available in health food shops and you might want to give them a try.