Pregnant women should always consult their physician before using any type of antihistamine. The risk of antihistamine use during pregnancy is based on the specific type of antihistamine being used. The U.S. Food and Drug Administration (FDA) publishes a comprehensive listing of risk categories for antihistamines, which includes risk factors to pregnant women. Only two categories of drugs, B and C, are currently available for use in the United States. The risk factors associated with these two categories are:

• Category B. There is no evidence in human studies that this category poses a risk to the fetus, and no animal studies have conclusively demonstrated that this category of antihistamines produces an adverse effect on the developing fetus. The FDA regards the risk associated with this category to be very low. Therefore, this is considered to be the safest type of antihistamine for use during pregnancy. This category includes chlorpheniramine, diphenhydramine, cetirizine and loratadine.
  
  
• Category C. While there are no human studies to rely on, animal studies have shown that this category of drugs can produce birth defects or the loss of pregnancy. This category of drugs includes fexofenadine and desloratadine.

While breastfeeding mothers should not be overly concerned with the use of antihistamines, they should still contact their physicians before taking the drug. The medication is passed through breast-milk, though it is in such a diluted form (one-hundredth of the original dose taken) that it should not represent a significant problem. While antihistamine use can lower the amount of milk produced by the new mother, this condition is not permanent.