Most women don't want to take unneccessary medications when they are pregnant. They fear deformities and problems due to medications. However who wants to be miserable months on end from allergies. The FDA doesn't deem any medications safe for pregnant women because no pregnant women want to be the ones tested on. There are categories of safety for pregnant women.
Medicine in category A have had lots of studies done and are deemed safe. There are not many in this category. Medicines in category B have been tested on pregnant animals, but not humans. They are deemed pretty safe. Medicines in category C may cause some effects, but the need for them out weighs the risks. Medicines in category D have definate risks to the baby, but sometimes are still needed. Category X medicines cause deformities to the baby and should not be sed by pregnant women.
Antihistamines are the preferred way to help allergies in pregnant women. They are a category B medication. This means that they are relatively safe and have been tested on pregnant animals. Claratin, Zyrtec, and levocetirizine fall into this category. Decongestants such as Sudafed are also preferred for oral decongestants for pregnant women. They should be avoided during the whole first trimester though because they can cause gastroschisis in infants. This is a problem where the intestines stick out of the body through a hole in the umbilical chord. It is caused by a rupured hernia in the abdominal wall, usually on the right side.
Decongestants fall into a category C medication. This means they can have some effects on the baby, but sometimes are still needed. Medicated nasal sprays also work for allergies. Usually you have to catch it before the allergy gets into your nose though. It is considered a category B medication. Rhinocart Aqua is about the only nasal steroid you can use. It is considered a category B medication. Allergy shots can be continued during a pregnancy. Do not start allergy shots while pregnant though. Usually doctors will cut the dosage of allergy shots in half while pregnant. Some doctors recommend you stop allergy shots though, because it can cause anaphylaxis. This is a life threatening reaction to the chemicals in the shot. This could cause problems to the baby. It is not always allergies that cause a drippy nose though. A sympton in the end of pregnancy is you sometimes get a drippy nose.