Which of the following oils should be avoided during pregnancy?

Fennel is an oil that should generally be avoided during pregnancy due to its hormonal effects. It is known to contain compounds that can mimic estrogen, which may potentially disrupt the hormonal balance necessary for a healthy pregnancy. Pregnant individuals are often advised to steer clear of substances that may induce or stimulate menstrual flow or contractions, and fennel's estrogen-like effects make it a concern in this context.

In contrast, while lavender, rosemary, and clary sage have their own cautions and potential effects, they are not universally contraindicated during pregnancy in the same manner as fennel. It's important for individuals to consult with a healthcare professional or aromatherapist to understand the specific safety profiles of different essential oils during pregnancy, but fennel stands out due to its distinct hormonal influence.