BACKGROUND: Gestational weight gain (GWG) plays a crucial role in maternal and fetal health outcomes during pregnancy. Excessive weight gain is associated with various complications, emphasizing the importance of effective management strategies. Nutrition counseling has been proposed as a promising intervention to optimize GWG and improve maternal and infant outcomes. The aim of this study was to evaluate the effectiveness of nutrition counseling for pregnant women experiencing unfavorable weight gain during pregnancy, who were referred to a registered dietitian at health centers in Iran. METHODS: A retrospective cohort study was conducted in Fars Province, Iran, involving pregnant women with unfavorable weight gain patterns referred to health centers between April 1, 2019, and November 20, 2023. Participants received either nutrition counseling or standard care. Data on maternal weight gain, infant anthropometric measurements, and counseling sessions were collected from the Integrated Health System. RESULTS: Among 565 enrolled pregnant women, 279 received nutrition counseling. Among pregnant women who experienced unfavorable weight gain and received nutritional counseling, 52.3% successfully attained a desirable weight gain. However, there was no significant difference in the hazard ratio of abnormal weight gain during pregnancy between the two groups. Additionally, no significant association were found in infant birth weight, length, or head circumference between the counseling and non-counseling groups. CONCLUSIONS: Nutritional counseling improved weight gain trajectories in pregnant women, with more achieving desirable weight gain. However, no significant differences were found in neonatal outcomes. Further studies are needed to refine intervention strategies. CLINICAL TRIAL NUMBER: Not applicable.