Background: Gestational weight gain (GWG) is one of the most important factors influencing pregnancy outcomes. Evidence indicates that too high or too low GWG is associated with several adverse maternal and neonatal outcomes both in the short and the long term. Although the latest research affirms the relationship between GWG outside the recommended guidelines and the incidence of negative pregnancy outcomes, previous studies were limited to specific ethnic groups such as American White and Black women and Asian women. This topic has not been examined with respect to the Arabic population, such as Omani women. Further, Oman’s Ministry of Health (MOH) antenatal care guidelines do not at present list GWG as a risk factor for adverse pregnancy outcomes. Purpose: This study examined the relationship between GWG (categorized into three groups) and maternal and neonatal outcomes among pregnant Omani women with normal prepregnancy Body Mass Index. Methods: This retrospective cohort study was conducted in the labor unit of Sohar New Hospital in North Al Batinah Governorate, Oman. All healthy women with normal prepregnancy Body Mass Index who had given birth to a singleton infant between August 1, 2021, and June 30, 2022, in the study settings were included in the study. Maternal and neonatal outcomes were retrieved from participants’ medical records using a standardized form. The analytical tools included descriptive statistics and the chi-square test. Results: Of the study population, 763 individuals met the inclusion criteria and were included in the study. Descriptive statistics showed that the mean score for the participants’ total GWG was 13.90 (SD = 4.63). In addition, 22.7% and 22.4% of the study participants gained weight above or below the Institute of Medicine recommendations, respectively. As for maternal outcomes, the findings from the chi-square test showed a significant association between total GWG and the incidence of emergency cesarean section (p .05), gestational diabetes mellitus (p .05), and pregnancy-induced hypertension (p .05). Moreover, the findings from chi-square test indicated a significant association between total GWG and six neonatal outcomes, namely macrosomia (p .05), small for gestational age (p .05), large for gestational age (p .05), low birth weight (p .05), intrauterine growth retardation (p .05), and preterm birth (p .05) Conclusion and Implications for Practice: Based on the high prevalence of GWG above or below Institute of Medicine guidelines and the clear adverse neonatal outcomes shown in this study, multiple recommendations are made. First, we recommend that Oman’s MOH includes GWG as a risk factor for pregnancy-related adverse outcomes. Second, we suggest that midwives closely monitor and manage GWG to ensure optimal pregnancy outcomes. Midwives should also provide continuous counseling and motivational health promotion interventions to facilitate lifestyle modifications such as a balanced diet and regular physical activities. Dietary supplements such as iron, folic acid, and multivitamins aimed at promoting normal GWG should be accessible to all pregnant women to reduce the impact of inadequate GWG on neonatal outcomes. Collaboration between MOH and the Ministry of Social Development is critical to identify women at risk of malnutrition and to provide them with necessary nutritional support during pregnancy.