Introduction: Gestational diabetes melitus (GDM) is one of the most common metabolic abnormalities in pregnancy and is a type of impaired glucose tolerance that is diagnosed during pregnancy. The purpose of the study was to assess the efficiency of counseling based on health promotion behaviors on fasting blood glucose and glucose tolerance test in overweight and obese pregnant women. Methods: This randomized controlled trial was conducted on overweight and obese pregnant women for prenatal care to the Rohani hospital in the Medical Science University of Babol, Iran, in 2018. Accordingly, a sample of 132 pregnant women was selected using convenience sampling and they were randomly allocated to experimental (n = 66) and control (n = 66) groups using encrypted cards. The interventions were performed in the experimental group within 4 weekly sessions lasting 90 minutes for one months based on the educational package of health promotion behaviors and the control group received routine prenatal care. The health promotion lifestyle questionnaire (HPLP2) and blood glucose test were utilized in pre-test (12 to 16 weeks of gestational age) and 2 months after the intervention ((24-28 weeks). The study was implemented during 6 months. The data were analyzed using MANCOVA in SPSS software.Results: Lifestyle modification training had significant effects on the mean score of the health promotion behaviors and incidence of
gestational diabetes mellitus at post-test (P <0.001). Comparison between groups showed that the difference in standard deviation fasting blood glucose after intervention in the two groups is more than 2, which indicates that counseling intervention based on health promoting behaviors has a considerable difference in glucose reduction. The mean of glucose in the glucose tolerance test after intervention was significantly lower in the counseling group than in the control group 126.97(22.48) versus 137.62(28.07) (P <0.001). Conclusion: According to the results, lifestyle modification training is effective on reducing the mean blood glucose level and increased the scores of different dimensions of health promotion behaviors, so it is recommended that planning and counseling according to the educational package be given in the prenatal care.