YARROW (Achillea millefolium) PREGNANCY CAUTION labor medicinal Generally considered a safe, nontoxic herb and is commonly used for: colds flus fevers PREGNANCY CAUTION: Because of its stimulation action on the uterus, it is one of the herbs that should NOT be used during the early stages of pregnancy. Yarrow, an excellent hemostatic, is used in combination with Shepherd'd Purse to arrest hemorrhaging during childbirth.