Asthma and seasonal allergy symptoms may worsen, improve, or remain unchanged during pregnancy. We can’t predict exactly how a pregnant woman’s body and hormonal changes alter how the immune system reacts to foreign substances. . . For example, pregnancy induces swelling of the nasal mucosa, the inner lining of the nose. Inflammation can lead to pregnancy rhinitis, or nasal congestion and a runny nose during pregnancy. . . Although the cause of pregnancy rhinitis is related to hormone production and not allergens, this condition may make pre-existing seasonal allergy symptoms worse.