First of all, every pregnant or nursing mother and her doctor must carefully weigh the benefits to the woman against the risks to her fetus or infant when using any medication. Always inform your doctor if you are pregnant, planning a pregnancy or breastfeeding before using any medicine. That being said, nasal steroids are generally well tolerated during pregnancy and by nursing mothers. Benadryl is probably the safest antihistamine to use because it's been around the longest, although it can cause drowsiness. Many of the newer antihistamines have either not been tested, or they have been found to be present in breast milk. Great caution should be used with all of these medications and certainly not before a thorough consultation with your doctor.