This study will evaluate the relationship between structured nutrition counseling, diet quality, and advanced glycation end products in pregnant women with gestational diabetes mellitus and women with normal glucose tolerance. Participants will be assigned to either a structured nutrition counseling group or a standard care group according to glucose tolerance status. The counseling program will include education and follow-up on healthy eating during pregnancy, gestational diabetes management, portion control, food choices, meal planning, and cooking methods. Diet quality, dietary habits, biochemical parameters, advanced glycation end products, gestational weight gain, and fetal outcomes will be assessed during follow-up.

Inclusion Criteria:

• Pregnant women aged 18 to 35 years
• Singleton and first pregnancy
• Gestational age between 24 and 28 weeks at enrollment
• Diagnosis of gestational diabetes mellitus or normal glucose tolerance
• Not using insulin therapy
• Stopped smoking at least 3 months before enrollment and not using alcohol
• Willingness to participate in the study
• Ability to provide written informed consent

Exclusion Criteria:

• Current use of insulin therapy
• Active smoking
• Alcohol use
• Refusal or inability to provide written informed consent

Eligibility is limited to pregnant women because the study focuses on gestational diabetes mellitus and pregnancy-related nutritional and metabolic outcomes.

Individual participant data will not be shared because the study includes sensitive health data from pregnant women. Data will be stored and analyzed in coded and anonymized form in accordance with the informed consent and ethics committee approval.

The laboratory personnel performing biochemical analyses will be blinded to group allocation. Participants and the dietitian delivering the intervention will not be blinded due to the nature of the nutrition counseling intervention.