Preeclampsia (PE) is a severe hypertensive pregnancy disorder characterized by endothelial dysfunction, placental ischemia and oxidative stress; however, reliable non-invasive biomarkers for early detection are limited. In this study, untargeted solid-phase microextraction with gas chromatography–mass spectrometry (SPME-GC-MS) was used to analyze volatile organic compounds in the urine of 45 women with PE and 46 healthy controls. Among the 29 metabolites identified, hexadecanal—a product of lipid peroxidation and sphingolipid metabolism—was found to be the most significant, with an area under the receiver operating characteristic (ROC) curve of 0.618, highlighting its diagnostic potential. This result emphasizes the role of hexadecanal in oxidative stress and placental dysfunction, which are central to the pathophysiology of PE. The results support hexadecanal as a potential non-invasive biomarker while demonstrating the efficacy of SPME-GC-MS in identifying metabolic disorders associated with PE, paving the way for further research to confirm its clinical utility for early diagnosis and risk assessment.