<p>Epidemiological studies have shown a statistically significant increase in lung cancer risk from prolonged exposure to indoor radon. While current radiation protection efforts address the general population, including workers in radon-prone areas, pregnant individuals represent a vulnerable subgroup that requires specific consideration. Prenatal exposure to ionizing radiation, including radon and its progeny, raises concerns not only for maternal health but also for potential in-utero tissue reactions and/or cancer development in other life stages in the offspring. This study aimed to develop a comprehensive biokinetic model for radon to evaluate fetal uptake following maternal exposure through inhalation. The model was based on the latest ICRP age- and sex-specific biokinetic model for radon, adapted to include pregnancy-specific compartments such as the uterus, placenta, arterial and venous cord blood, and key fetal organs (lungs, brain, kidneys, thyroid, bone surface, liver, and adipose). Transfer rates were calculated using Fick’s law of passive diffusion. Maternal and fetal physiological changes throughout pregnancy, including tissue masses and blood flows, were incorporated. Model simulations show that, despite radon gas being predominantly exhaled after inhalation, a fraction crosses the placenta, reaching fetal tissues—particularly those with higher fat content. Additionally, due to the chemical affinity of radon and fatty tissues, fetal adipose tissue receives a significant proportion of radon, resulting in the highest predicted uptake among fetal tissues. This biokinetic model provides an approach to estimate fetal uptake of radon from maternal exposures, supporting more accurate assessments for radiation protection of pregnant individuals and their developing fetuses.</p>