Hives, or urticaria, are uncomfortable skin symptoms that may occur during pregnancy. The condition may arise for reasons such as an allergic reaction to a food or medication, or as an immune-system phenomenon. Hives appear most often when a substance called histamine is released as mast cells or related basophils, a type of white blood cell, become more active in the blood stream. When hives are not the result of an allergy during pregnancy, the pregnant mother's hormones may be responsible for the outbreak. Hives are not dangerous to the mother or baby, but they can be quite debilitating from the constant itching.
Hives look like raised red or pale-colored welts on the skin. They cause severe itching and can migrate from area to area over the course of time. They may even be accompanied by localised swelling, called angioedema. A doctor should always evaluate the appearance of the hives to distinguish them from other pregnancy-associated rashes such as autoimmune progesterone dermatitis of pregnancy and pruritic urticarial papules and plaques of pregnancy, or PUPPS. An allergist or immunologist may be called on to perform allergy testing, if needed, to help determine the cause.
Pregnancy-associated hives are usually easily managed with over-the-counter antihistamines. Your doctor may suggest diphenhydramine, sold as Benadryl; loratidine, known as Claritin; or cetirizine, sold as Zyrtec. Occasionally, more aggressive treatment may be necessary to control and eliminate the symptoms. It is always best to make sure your obstetrician is aware of your hives and of any medications that you may be taking to treat them.