The American Journal of Obstetrics and Gynecology reports that pregnant women who consume 200 milligrams or more of caffeine a day the amount in 10 ounces of coffee or 25 ounces of tea may double their risk of miscarriage. The lead author of the study, Dr. De-Kun Li, a reproductive and perinatal epidemiologist at the Kaiser Permanente Division of Research in Oakland, California, suggests that pregnant women may want to reduce their intake or cut it out entirely. "Stopping caffeine really doesn’t have any downside," Li said.

It is well known that caffeine crosses the placenta and reaches the developing baby, which cannot metabolize caffeine like an adult. For this reason, there has been much controversy on how much caffeine is safe for the developing baby if any at all. But this is the first study which links caffeine and miscarriage.

Recently the American Pregnancy Association weighed in on the benefits of drinking herbal tea during pregnancy and concluded along with several recent studies that not only do most herbal teas pose no risk to the developing child and mother, but herbal teas can also play a central role in strengthening the uterus muscles, decreasing the length of labor and decreasing the number of interventions used such as artificial rupture of membranes (AROM), assisted delivery, and cesarean delivery, as well as provide important vitamins and minerals like calcium, iron, vitamin D, K and C. They do, however, caution that expecting mothers should consult with their midwife or Doctor before starting a strict regimen of herbal tea.