Gestational diabetes mellitus (GDM) is a carbohydrate metabolism issue during pregnancy that is dangerous for mother and the baby. GDM occurs in 1 out of 3 diabetic women in 16.2% of live births. GDM knowledge and treatment practices among nurses were found inadequate when nurses’ effectiveness in treating a disease they have a shallow knowledge about (GDM) was investigated in the local medical facility. A GDM instructional module was applied and its effectiveness in promoting nurse’s use of GDM education as a treatment strategy tested. The total concept for knowledge and care, empowerment and the social cognitive theories grounded this research. Methodology was Mixed. A population/patient problem-intervention-comparison-outcome-time (PICOT) design was applied in the analysis of data from a sample size (n = 40), whereby the treatment group (TG = 20) had an intervention, and control group (CG = 20) did not. Data was analyzed descriptively and inferentially with t-test statistic, including the Cohen’s d test for effect size. Evidence showed a significantly high post-intervention gain in scores CG and TG, higher among DNPs than other nurses. Also, the Cohen’s d test indicated high magnitude effect size. Overall confidence in GDM treatment method improved. A comparison of mean test completion time and scores indicated that TG completed the posttest at a shorter time than CG. Knowledge improvement results were TG 27%; CG 2%. GDM education is an effective path to positive social change, beneficial to nurses, the medical facility and the community. Improved GDM treatment means a healthier population and increased productivity for the community. GDM education is non-medicated and more affordable—a huge savings for the community.