There are a lot of mixed views on the safety of caffeine in pregnancy. This uncertainty may come from the mixed research results. Two immediate, probably uncontrollable flaws of caffeine research are, it is based on maternal recall/truthfulness and the inability to know the true caffeine levels consumed. This makes interpreting the results more difficult.
What we do know is that caffeine readily crosses the placenta, and mothers metabolize caffeine more slowly during pregnancy. Currently, ACOG recommends caffeine intake remains below 200mg a day. A brewed drip cup of coffee has about 137mg of caffeine in 8oz (though their cited source now says 95 mg) and tea is estimated to be about 48 mg. In ACOG's opinion, there does not seem to be a clear risk between moderate caffeine consumption and miscarriage, but they also don’t feel they can raise the recommendation higher at this point. ACOG also does not find a definite link between caffeine and preterm birth. More research is needed to see if there is a correlation between caffeine and intrauterine growth restriction.
I keep seeing a reference to the World Health Organization recommending less than 300mg per day, but I have yet to find this in a document. The only thing close was a WHO European document from 2001, recommending intake be no more than 3-4 cups of coffee a day. (If anyone finds a proper source, please let me know!)
While ACOG looked at two large studies in regards to caffeine and miscarriage, a recent meta-analysis included 14 studies. The authors' conclusion was high levels of caffeine consumption (>350mg per day) was related to increased miscarriage risk.
In looking at low birth weight, another meta-analysis found that high levels of caffeine were associated with lower birth weight. High level was not defined. 13 studies were included.
This was the only study I could find related to a possible increase risk of preterm birth. It seems there might be an association between preterm birth and Japanese and Chinese Tea; soft drinks and coffee did not have the same effect.
It appears that 200-300mg of caffeine a day is safe during pregnancy. Knowing this, it is a good idea to consider all sources, and know the amount you consume.
For someone who personally loves coffee, limiting my consumption during pregnancy is tough, especially once the nausea subsides. Part of the love is related to the feeling of a warm mug in hand, so I try to find some substitutes. I will make my coffee half decaf. And while drinking a cup of total decaf coffee is often not palatable, I do like decaf black tea. This year I have tried hot water with lemon and honey. Though not my loved cup of coffee, overall it hits the warm mug in hand spot.
Thoughts of caffeine? Any good substitutes you have found?