Allergic reactions in pregnant women

Allergic reactions in pregnant women: Changes in the immune system

Pregnancy is a time of profound changes throughout the body, and the immune system is no exception. It undergoes a complex remodeling, aimed at not rejecting the fetus, which is for it half “foreign”. This remodeling can unpredictably affect the course of pre‑existing allergic diseases or even trigger the onset of allergy for the first time. It is important to understand that each woman's reaction is individual.

Immune shift: “Rule of thirds”

The impact of pregnancy on the immune system is often described by the so‑called “rule of thirds”, which is especially well known for bronchial asthma, but also applies to other allergic conditions:

• In one third of women the condition improves: Allergy symptoms become less pronounced or disappear completely. This is related to the natural suppression of certain immune pathways.
• In one third of women the condition remains unchanged.
• In one third of women the condition worsens: Symptoms become stronger and reactions sharper.

Underlying these changes is the so‑called “Th2 shift” – a dominance of one type of immune response over another, which generally increases susceptibility to atopic reactions.

Why is this important?

The main challenge with allergic reactions during pregnancy is the need for careful selection of treatment. Many commonly used anti‑allergy medications are contraindicated or not recommended, especially in the first trimester. Any treatment, even topical, must be coordinated with a physician. Read about general principles in the article "Medications during pregnancy".

Allergic reactions can manifest in various ways: from nasal congestion and eczema flare‑ups to more serious conditions. It is important to distinguish allergy symptoms from other common “pregnancy” symptoms, which can sometimes be difficult without a doctor's help.