Despite the ever-growing body of research on essential oils, there is only a limited amount of study conducted on essential oil use during pregnancy - this owing to the unethical nature of conducting research on pregnant women.
The quick answer, though, is yes, many essential oils do cross the placenta (and cell membranes, and the blood brain barrier), which is why it is especially important to be mindful of essential oil concentration and purity during pregnancy. (Tillett & Ames, 2010)
The placenta provides a natural barrier against positive and neutral molecules and molecules with weight more than 1000 atomic mass units (AMUs). Since essential oils weigh less than 250 AMUs and many are negatively charged, it is fair to assume that essential oils cross the placenta. Despite this, there is virtually no evidence that, when used correctly, essential oils have a negative impact on the fetus in utero. The immaturity of the fetal liver may even offer a degree of protection, since fetuses are not capable of metabolizing compounds into more toxic forms, a process which requires phase two liver enzymes.
It is an important side note that the U.S. government does not oversee essential oil quality except to stipulate that only 5% of a product be pure essential oil to be labeled “pure”. This is a disappointment to many essential oil enthusiasts, who believe that the integrity of essential oil quality is at the heart of essential oil therapy. The level of quality is indeed what distinguishes essential oils used for therapy from, say, public bathroom air freshener.
If you are having any doubts whatsoever, don't give up on essential oils during pregnancy just yet. Their incredible benefits far outweigh any effort it may take to understand safe use. Consider a few of the studied benefits for use during maternity: Of 23 patients evaluated in a controlled study on lavender for feelings of anxiousness during induction of labor, a significant number of moms were found to have reduced feelings of anxiousness, ache to head, and interrupted sleep (Adams 2000); Sitz baths with lavender essential oil were found to significantly decrease inflammation and discomfort compared to the control group using povidone-iodine sitz baths (Complementary Therapies in Clinical Practice 2010). There are diaper buckets full of studies on pain relief during labor, reduced nausea during pregnancy, and other maternity-related topics as well. This simple, lovely practice has the potential to change someone's outlook, quality of life, or length of labor with little risk of harm.
Essential oil authors and medical professionals, including Ron Guba, Robert Tisserand, and Jane Buckle agree that with attention to dose and quality, "it is more prudent to recommend that those which are potentially dangerous be avoided throughout pregnancy", than to limit responsible use of essential oils during early pregnancy. [Tisserand]
If you would like to learn more about using essential oils during maternity, postpartum, or infant care, use the button below to visit my website and access our community forum, webinars, Birth Kit Mama training program or professional program.