Aromatherapy is a powerful but very safe option for providing comfort to a laboring woman. The essential oils used in labor can also be very beneficial in the postpartum period when most women experience at least some measure of the "baby blues." Certain oils can also be used during pregnancy, but you should talk to your care provider about your specific situation and any contraindications with aromatherapy.
I thought I would share what I have personally used both at my own births and for some of my clients. Essential oils in general are fairly inexpensive so it's easy to get started with a handful of oils you love.
It's important to remember and be sensitive to the fact that a laboring woman's senses are heightened, especially her sense of smell. There may be scents she normally enjoys that become repugnant during labor, or, she may even begin to dislike a scent she had asked for in earlier labor. So be sure to use methods that can be "dialed down" fairly quickly. Whereas in day to day life I might scent a bath by putting drops of oil into the bathwater, in labor I typically use a basin of warm water or even the bathroom sink so that if she becomes annoyed by the scent it can be quickly removed. Cotton balls or tissues are an excellent way to give mothers a whiff without scent overpowering the entire room. I carry unscented massage oils and add drops of essential oil only after checking in with the mother and mix it in my palm. It's great if a pregnant woman can experiment with the scents of different oils so that she knows ahead of time which ones she likes. Still, be sure to check in with the laboring mother anytime you are planning on using oils by asking her if that's all right, and maybe giving her a choice between two. Do NOT ask her to tell you which oil she'd like out of seven options or to answer a complicated question about it. This is a surefire way to have aromatherapy harm more than it helps.
Lavender: This one is a favorite of doulas and midwives because it promotes relaxation. It can be used on a cotton ball or electric diffuser if the mom really likes it, or it is wonderful in the tub. Again, use a basin full of warm water or the bathroom sink and add 2-4 drops. Don't add it directly to the bathwater in case the mother suddenly doesn't enjoy the scent, and it's also a good idea not to add anything to bathwater of a woman whose membranes have ruptured. Remember that this is a heady, relaxing scent, so it is best used either in early labor when everyone is trying to get a little rest, or in highly stressful, charged times like transition. Lavender can also be used to help alleviate nausea. It is not a good idea to break out the lavender in the middle of an especially long active stage where everyone is exhausted already when something more energizing might be beneficial. Lavender is an excellent oil for new mothers to have on hand. I have used it in the bathroom when giving my children baths to help wind them (and me!) down for the evening. A few drops on the mother's pillow can help induce relaxation to let a stressed out mother drift off to sleep. Lavender is a key ingredient in the postpartum comfort pads recipe.
Peppermint: Peppermint can be a very powerful, invigorating oil and is quite versatile. For a woman exhausted by the rigors of labor, a foot and leg massage with a few drops of peppermint oil blended in your favorite unscented oil (I like sweet almond) can be energizing and blissful for tired muscles. Peppermint oil can be used directly on the temples to relieve headaches, but check with your care provider first as using essential oils topically is somewhat controversial. For a woman who is having a difficult time passing urine either during labor or after birth, a few drops of peppermint oil put directly into the toilet bowl can help relax the urethra. Peppermint (and spearmint) are also useful for treating nausea.
Citrus: Some options here include Grapefruit, Orange, Lemon, or Neroli which is wonderful but highly expensive. Grapefruit is fresh and invigorating and perfect for an exhausted labor room. Orange can be combined with peppermint and lavender or used on its own for nausea. Lemon is very refreshing and great for masking any other unpleasant smells.
Florals: I don't personally enjoy many of the floral scents, but lots of people do. The most popular ones for labor include Geranium and Ylang Ylang.
While I have advised using transport methods that can be easily reversed for aromatherapy during labor, there are a couple of exceptions. When first checking into the hospital, if the room smells antiseptic or stale, an aromatherapy mist can be invaluable. Similarly, if a laboring woman (or her partner!) has been vomiting, a mist can help freshen the air. I use a dark blue glass bottle (essential oils are to be kept protected from light) and use 10-15 drops per 6-8 oz. of water.
One of the wonderful things about aromatherapy is the effect it has on everyone in the room, not just the laboring mother. The person giving the scented massage inhales the aroma and benefits from the healing properties just as the person receiving it. One of the most important part of the doula's role is something Pam England (author of Birthing from Within) calls "Holding the Space" which refers to safeguarding the birthing woman's space, keeping it an appropriate atmosphere for giving birth. Instinctively, mammals seek out places that are dark, protected, and overall safe to birth. Nurses and any other caregivers that come into a birth room with dim lights and lovely aromas instantly sense the sanctity of this space and will usually behave in a way that is very respectful. These caregivers also receive the benefit of a little aromatherapy to break up their busy workday, and who wouldn't like that?
If you are interested in learning more about aromatherapy, check out Aromatherapy and Massage for Mother and Baby by Alison England. There are some wonderful labor mist recipes here by Demetria Clark. Be sure to check out the AromaWeb!