[en] Some of the procedures for diagnostic or treatment used in the medicine use radioactive materials as the I¹³¹. By means of Monte Carlo methods were calculated the doses in the internal organs of a woman, with three months of pregnancy, due to the radioiodine captured by her thyroid, as well as to 1 meter of the gland. A three-dimensional mathematical model of the body of a woman was used and by means of Monte Carlo, the radioiodine photons were transported isotropically from the thyroid toward the whole body and was calculated the absorbed dose by their internal organs, also the Kerma in air (K) was determined and the environmental equivalent dose (H^*(10)) at 1 m of the gland. Two activity factors at dose were determined, Gamma Factors that it allows to estimate the dose that the patient produces to people to its around. Of the gamma radiation that emits the I¹³¹ in the thyroid was found that the thymus receives the biggest dose while the uterus is the organ that smaller dose receives. The determined gamma factors were: Γ_KAire = 56 μGy-m²-h^-1-GBq^-1, and Γ_H^*₍₁₀₎ = 73 μSv-m²-h^-1-GBq^-1. The distribution of the absorbed dose by the internal organs is attributed to the relative distance among the thyroid and the other organs, to the inter-organs shielding, its size and to its elementary composition. The Γ_KAire and Γ_H^*₍₁₀₎ factors allow to estimate the exposure that the patient produces on the personnel to its around. With this, the nuclear medicus, the medical physicist or the one responsible of the radiological safety in the hospital can give more precise indications on the behavior of people around the patient. (Author)