Background: Nausea and vomiting in pregnancy (NVP), or emesis gravidarum, is a frequent complication of early gestation with unclear causes, suspected to involve genetic, hormonal, and gastrointestinal factors. Our study investigated the association of human chorionic gonadotropin (hCG), histamine, diamine oxidase (DAO), thyroxine and pyridoxine and the severity of NVP symptoms and assessed the efficacy of a vitamin C-containing chewing gum as a potential NVP treatment. Methods: In this prospective, double-blinded, randomized, controlled trial, 111 participants were assigned to receive vitamin C-containing chewing gum, placebo gum, or no treatment at two follow-ups during early pregnancy. Maternal serum levels of hCG, histamine, DAO, thyroxine, and pyridoxine were measured and correlated with NVP severity using the Pregnancy-Unique Quantification of Emesis and Nausea (PUQE-24) score. Results: Elevated maternal hCG levels were significantly associated with an increased PUQE-24 score (p < 0.001), while histamine levels showed no significant correlation (p = 0.68). Maternal DAO levels negatively correlated with NVP symptoms (p < 0.001) and elevated thyroxine (p < 0.001) and pyridoxine levels (p < 0.001) were associated with increased PUQE-24 scores. The vitamin C-containing chewing gum did not demonstrate efficacy in alleviating NVP symptoms compared to placebo gum or no treatment during the first (p = 0.62) and second follow-up visits (p = 0.87). Conclusions: Our study underscores the complexity of factors contributing to NVP, highlighting the significant roles of hCG and DAO, while histamine levels appear unrelated. Maternal thyroxine and pyridoxine levels also significantly correlate with NVP symptoms. Vitamin C-containing chewing gum was not effective as a treatment for NVP. Further large-scale studies are needed to better understand these interactions and develop targeted treatments in the future.