It seems that studies have shown various outcomes, and most recommendations suggest erring on the side of caution when it comes to caffeine consumption during pregnancy.
Moderate caffeine consumption (less than 200 mg per day) does not appear to be a major contributing factor in miscarriage or preterm birth. The relationship of caffeine to growth restriction remains undetermined. A final conclusion cannot be made at this time as to whether there is a correlation between high caffeine intake and miscarriage.
American College of Obstetricians and Gynecologists
Due to conflicting conclusions from numerous studies, the American College of Obstetricians and Gynecologists and the March of Dimes recommend that until more conclusive studies are done, pregnant women should limit caffeine intake to less than 200 mg per day. This is equal to about one 12 oz cup of coffee.
American Pregnancy Association
Caffeine does cross the placenta. Also, remember that caffeine is present in many other foods besides coffee. Caffeine can be found in tea, chocolate, soda, and even some over the counter medication for headaches.
Please consult your doctor about whether you should stop or limit your caffeine intake. As we’ve seen in other studies, people’s bodies can react and metabolize caffeine in very different ways, and that can apply to the baby as well.
The following study showed that even moderate caffeine intake affected birth weight.
Pregnant women who consumed the caffeine equivalent of as little as half a cup of coffee a day on average had slightly smaller babies than pregnant women who did not consume caffeinated beverages, according to a study by researchers at the National Institutes of Health.
National Institutes of Health