What could it mean if you get hives when you get your menstral period?

Urticaria: Urticaria, or hives, can occur during times of stress - both physical and emotional. Menstruation can cause both. Hives, as with most allergic reactions, are additive, meaning that little thing you may be allergic to (food coloring, pollen, etc) may add up to a flare-up, and worsen with stress. Controlling some of these with antihistamines (claritin, benadryl, (diphenhydramine) etc) may help.

Hormone related: It's probably hormone related. It can happen after you stop taking birth control pills. This would mean you have been sensitized to female hormones, estrogen and/ or progesterone. In other words, you have developed allergy to your own hormones. skin problems can worsen during the premenstrual period, including acne, herpes simplex, and autoimmune conditions.

May not be allergy!: Hives that worsen with your mestrual cycle are probably not allergy related. Chronic hives are most commonly a form of autoimmunity. Hives are caused by mast cells releasing histamine. There are multiple triggers for mast cells to do this, most famously an allergic reaction. Other triggers could be heat, cold, viral infection, autoimmune antibodies, narcotics, etc. Hormones may play a role.