A recent study found that pregnant women that drink more than one cup of coffee a day are at risk of having a miscarriage. Even a small amount can be very dangerous. Two hundred milligrams of caffeine, the equivalent of two cups of regular coffee, can double the risk of having a miscarriage, especially in the first trimester. Caffeine decreases blood flow to the placenta and stresses the metabolism of the fetus. It is recommended that a pregnant woman doesn’t have any caffeine in her diet.