Autoimmune thyroid disease (AITD) is the leading cause of thyroid dysfunction globally, characterized primarily by two distinct clinical manifestations: Hashimoto’s thyroiditis (HT) and Graves’ disease (GD). The prevalence of AITD is approximately twice as high in women compared to men, with a particularly pronounced risk during the reproductive years. Pregnancy exerts profound effects on thyroid physiology and immune regulation due to hormonal fluctuations and immune adaptations aimed at fostering maternal–fetal tolerance, potentially triggering or exacerbating AITD. The impact of AITD on pregnancy outcomes is multifaceted. Both HT and GD have been associated with adverse obstetric and neonatal outcomes, including miscarriage, preterm delivery, preeclampsia and fetal growth restriction. Inadequately managed AITD can also affect fetal neurodevelopment due to disrupted maternal thyroid hormone availability during critical periods of brain maturation. This review explores the complex interplay between the genetic, epigenetic and environmental factors that drive AITD during pregnancy, highlighting their roles in disease development and impacts on pregnancy outcomes. Gaining a deeper understanding of these mechanisms is crucial for improving diagnostic tools, treatment options and preventive measures to enhance the health and well-being of both the mother and the newborn.

Autoimmune thyroid disease (AITD) is the most common organ-specific autoimmune disorder clinically presented as Hashimoto thyroiditis (HT) and Graves’ disease (GD). The pathogenesis of AITD is caused by an inappropriate immune response related to genetic, non-genetic, and environmental factors. Pregnancy is one of the factors that have a great influence on the function of the thyroid gland because of the increased metabolic demand and the effects of hormones related to pregnancy. During pregnancy, an adaptation of the maternal immune system occurs, especially of the innate immune system engaged in maintaining adaptive immunity in the tolerant state, preventing the rejection of the fetus. Pregnancy-related hormonal changes (estrogen, progesterone, hCG) may modulate the activity of innate immune cells, potentially worsening the course of AITD during pregnancy. This especially applies to NK cells, which are associated with exacerbation of HD and GD. On the other hand, previous thyroid disorders can affect fertility and cause adverse outcomes of pregnancy, such as placental abruption, spontaneous abortion, and premature delivery. Additionally, it can cause fetal growth retardation and may contribute to impaired neuropsychological development of the fetus. Therefore, maintaining the thyroid equilibrium in women of reproductive age and in pregnant women is of the highest importance.