The best guide to use during pregnancy is The Gentle Babies Book, but here is a quick guide you can use if you do not have this book:

Oils to avoid during pregnancy: Basil, Birch, Calamus, Cassia, Cinnamon bark, Hyssop, Idaho Tansy, Lavandin ( a form of lavender often sold in stores) Rosemary, Sage and Tarragon.

Also avoid Peppermint durig the third trimester as it has been known to possiblly turn the baby. Clary Sage has been known to create contractions.