Purpose <p>This study aimed to evaluate the image quality-dose trade-off in pregnant patients imaged with long-axial field-of-view [¹⁸F]FDG PET/CT and to identify the most predictive body composition metric for image quality to develop a pregnancy-tailored dosage model.</p> Methods <p>Patients imaged with [¹⁸F]FDG PET/CT according to local pregnancy protocols were included in this study. Using raw PET data, images of various degrees of image quality were reconstructed. Acceptable image quality was identified using signal-to-noise ratio (SNR) in the liver and Likert scores. The minimum required scan statistics was modelled based on SNR and patient body composition. F-tests were used to find the best-fitting model parameter out of weight, weight-to-height-ratio, body-mass-index, and body surface area (BSA). Foetal dose was estimated with PET conversion factors and size-specific CT dose index values.</p> Results <p>Eleven patients were included in image quality analysis and dosage model optimization. SNR strongly correlated with Likert scores (R² = 0.80), with 10.72 SNR indicating acceptable image quality. BSA best predicted image quality (R² = 0.85), outperforming weight (R² = 0.78), weight-to-height ratio (R² = 0.63), and body mass index (R² = 0.38). The proposed dosage model reduces activity by 41–96% compared to current local pregnancy and adult protocols, resulting in estimated foetal radiation doses of 0.066 mGy (PET) and 0.31 mGy (CT).</p> Conclusion <p>BSA accurately predicted [¹⁸F]FDG PET/CT image quality in pregnant patients. The proposed dosage regimen allows significant dose reduction and can be used as a foundation for the development of pregnancy dosage protocols.</p>