2. May cause birth defects
According to several studies, drinking excess green tea during pregnancy may have a negative impact on the mother and the unborn. Consuming more than 300 mg of caffeine per day increases the risk of hypertension during pregnancy. Scientists discovered that caffeine and tannins in green tea can reduce the levels of folic acid. However, folic acid is a water-soluble B-vitamin that prevents miscarriages and birth defects like spina bifida.