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It is sometimes necessary to take an antihistamine during pregnancy. Pregnancy is an uncomfortable time, and allergies can make it worse. Taking an antihistamine during pregnancy can be safe, as long as it is used as directed.
Antihistamines halt allergic reactions by preventing the action of histamines. Histamines are released by the immune system in response to what it interprets as attacking organisms. They cause cells to expand and leak fluid, and also cause capillaries to dilate. Antihistamines prevent histamines from binding with cells and causing these reactions, though histamines will still be produced.
There are both over-the-counter and prescription antihistamines available. It is safe to take both kinds of antihistamine during pregnancy as long as a health care provider has been consulted. Other allergy products may not be safe to take. Patients with high blood pressure during pregnancy may not be able to use antihistamines.
Even patients who do not usually take antihistamines might find the need to take an antihistamine during pregnancy. Some women report a worsening of allergy symptoms while pregnant. Many women experience nasal congestion during pregnancy, which can make allergies seem worse. It is not uncommon for women to develop new allergies while pregnant.
All drugs are given a category according to how they affect an unborn baby. Category A drugs are safe. There have been multiple studies showing no harm to the fetus when these drugs are taken by pregnant women. Category B drugs have been shown to cause no ill effects when taken by humans or animals during pregnancy, or studies show negative effects in animals but no negative effects in humans. Drugs in category C have not had sufficient studies done to determine safety or animal studies have shown negative effects, but there have been few or no studies done to determine the effects on the human fetus.
Category D drugs have been shown to cause harm during studies, but the benefit of use can outweigh the risks. Drugs in category X have been shown to have extreme negative effects on the fetus, including termination. These drugs must never be taken during pregnancy.
Many antihistamines are in category B, and some are in category C. The effects that allergy symptoms, particularly breathing difficulty, can have on a fetus are probably outweighed by any risks posed by category C antihistamines. Even though they are considered safe, a health care provider should be consulted before taking an antihistamine during pregnancy.