Pregnant women are urged to use caution when using essential oils. First and foremost, it would help to consult with a fully qualified aromatherapist before beginning anything. Some have said that pregnant women simply should not use aromatherapy at all, and this is still the case if you are at risk for miscarriage of other complications. However, if used properly, it is now considered to be okay after the first trimester. A study by Oxford Brook's University found that aromatherapy actually improves a sense of well being and can be used to reduce anxiety and fear, two things that can make labor harder.
Some helpful hints about aromatherapy when pregnant: a little bit goes a long way; use with care, and don't put the oils undiluted on your skin. The oils are great when mixed with lotion for a massage, or when a few drops are added to a bath. There are, however, several essential oils that experts say you should avoid throughout your pregnancy, including: cinnamon, sage, thyme, fennel, peppermint, rosemary, and wintergreen. Again, talk with somebody that is familiar with these natural methods before using anything.
What's interesting is that the physical effects of relaxation or invigoration may also be learned. In fact, these same "chemicals of well-being" are also released when talking to a lover or listening to music. That's where the idea of personal aromatherapy comes in.