Background: Appropriate weight gain during pregnancy is crucial for maternal and fetal health. This study aimed to identify factors associated with achieving recommended weight gain among pregnant women in Deli Serdang Regency, North Sumatra, Indonesia. Methods: A cross-sectional study was conducted in 2023 involving 248 pregnant women in the third trimester at five health centers in Deli Serdang Regency, North Sumatra. Data were collected through structured interviews and questionnaires covering demographic factors, knowledge, behavior, and nutritional intake. Weight gain during pregnancy was recommended based on IOM recommendations. Analysis was performed using the Chi-square test and multinomial logistic regression with 95% confidence intervals using SPSS version 26. Results: The study looked at how gestational weight gain was affected by various factors. Significant factors linked to recommended weight gain included energy, protein, fat, and carbohydrate intake, physical activity, knowledge, perception, and family support (all with p-values less than 0.05). However, maternal age, education, job, income, number of previous births, and smoking habits did not significantly affect weight gain. Pregnant women who consumed enough energy (AOR = 0.188, P = 0.006), low-fat (AOR = 0.204, P = 0.031), and enough carbohydrates (AOR = 0.065, P = 0.045) were less likely to gain too little or too much weight. Physical activity was very important: light (AOR = 0.133, P < 0.001) and moderate (AOR = 0.250, P = 0.001) exercise lowered the risk of gaining less weight than recommended. Low physical activity increased the risk of gaining too much weight (AOR = 3.458, P = 0.039), and was the strongest factor affecting weight gain. Additionally, poor pregnancy planning increased the risk of gaining too much weight (AOR = 2.328, p = 0.048), and low family support raised the risk of gaining too little weight (AOR = 2.571, P = 0.023). Conclusion: Physical activity is the most influential factor in achieving recommended weight gain; the more active the pregnant woman is, the greater the chance of achieving the appropriate weight. © Iran University of Medical Sciences. This work has been published under CC BY-NC-SA 4.0 license.