I found this article some time ago and think it's very useful. When I drink tea I always have Camille tea which seems to be harmless during the pregnancy.
Article:
How can I tell which herbal teas are safe to drink during pregnancy?
Although no U.S. regulation specifically addresses herbal tea, most of the herbs the FDA considers safe for food use are presumed safe for tea as well. This may or may not be the case.
Teas made from herbs like peppermint and thyme may be safe to drink occasionally in small amounts while you're pregnant or nursing. But drinking excessive amounts of any tea can cause health problems for you and your developing baby. The herbs in teas are more concentrated than in food, so drinking them may be harmful even if eating them isn't.
There's not much research about the safety of herbal products, so if that's a concern, it's probably best to steer clear of all herbal teas while you're pregnant and nursing. If you choose to drink them, do so in moderation and let your doctor know beforehand so you can be sure they're safe for you and your baby.
Which teas are not safe?
Many herbs used in teas, when taken in large or medicinal amounts, can be harmful. Some may even increase the odds of miscarriage, early labor, or low birth weight.
Herbs that may cause problems include anise, ginger, lime blossom, rose hip, catnip, chamomile, comfrey, ephedra (called ma huang in traditional Chinese medicine and banned in the U.S. since 2004), European mistletoe, hibiscus, horehound, Labrador, lemongrass, licorice root, mugwort, pennyroyal, raspberry leaf, rosemary, sage, sassafras, stinging nettle leaf, vetiver, and yarrow.
Ginger is commonly used to ease morning sickness during pregnancy, and studies have shown its effectiveness and safety for this purpose. But there's also some evidence that it may negatively affect fetal sex hormones. So before you drink ginger tea, be sure to discuss its benefits and risks with your healthcare provider.
Although some midwives use raspberry leaf (also known as red raspberry leaf) to aid delivery, its effectiveness hasn't been proven. It should be used only near term and under the supervision of a healthcare professional. Avoid the rest of the herbs mentioned above if you're pregnant or nursing.
Note: You can still eat food that contains some of these herbs, like rosemary and anise, because the amounts used in food are generally much smaller than those used in tea—and not as potent. (The brewing process for making tea concentrates the chemicals of the herbs.)
Other reasons to avoid certain herbs used in teas:
Coca (also known as mate de coca) may contain small amounts of cocaine, according to the U.S. Drug Enforcement Administration (DEA).
Comfrey, kava root, and woodruff may damage your liver.
Mate (or yerba mate) can contain as much caffeine as coffee.
None of these herbs should be taken while you're pregnant or nursing.
What about the herbal teas that are marketed to pregnant women?
The same cautions apply to teas made specifically for pregnant women, which are sold in supermarkets and health food stores. While the makers of pregnancy teas promote their products as healthy for expectant moms, no clinical studies support these claims, and the safety of the ingredients is not regulated.
Pregnancy teas usually include ingredients such as alfalfa, fennel seed, lemongrass leaf, lemon verbena, nettle leaf, rosehips, and strawberry leaf. Not all of these are safe to take during pregnancy. For example, nettle leaf (also known as stinging nettle leaf) stimulates the uterus and can cause miscarriage.
How can I choose a safe herbal tea?
If you enjoy herbal teas, check package labels and steer clear of unsafe or unfamiliar ingredients. Or consider making your own: Add honey, fruit juice, lemon rinds, cinnamon, or cloves to boiling water or decaffeinated black or green tea.
Even homemade teas are best in moderation because not enough is known about the effects of most herbs on pregnant and breastfeeding women. And never make a tea from any plant unless you're 100 percent sure you know what it is and that you can safely take it while you're pregnant.