When performing [18F]FDG PET scans on pregnant patients, it is crucial to carefully weigh the risks and benefits of the procedure to the fetal dose. This work aims to simulate fetal dose in a 24-week pregnant woman using the Geant4 Application for Tomography Emission (GATE) toolbox. We use an anthropomorphic virtual simulator, Katja, and a realistic activity distribution of [18F]FDG with and without voiding regimes. The total fetal dose due to [18F]FDG uptake in the mother was 0.005190 mGy/MBq, with 19.2% due to positron emission and 80.8% due to gamma emission. The total fetal dose due to the fetus uptake was 0.000257 mGy/MBq, with 16.7% due to positron emission and 83.3% due to gamma emission. The contribution of the dynamic bladder and static bladder to the total fetal dose was 15% and 19%, respectively. The fetal doses considering bladder voiding models were 0.00079 mGy/MBq for dynamic voiding and 0.00109 mGy/MBq for no voiding. We conclude the fetal dose from [18F]FDG administration is low during the second trimester of pregnancy, and it can be reduced with the stimulation of bladder voiding.