According to Drugs.com, green tea should not be consumed during pregnancy. Women who plan to breastfeed upon delivery should consult a medical practitioner to discuss the risks that consuming this beverage poses to infants.
According to Health.com, green tea contains tannins, which can decrease the absorption of folic acid in the body. Folic acid is an important nutrient that pregnant women need as it helps decrease the likelihood of the fetus developing birth defects. Black tea should also be avoided during pregnancy as it has similar effects. Health.com also notes that green tea can disrupt the absorption of iron in the body.