How to manage Gestational Diabetes Mellitus (GDM) with Medical Nutrition Therapy (MNT) and initiate insulin therapy?

Management of Gestational Diabetes Mellitus: Medical Nutrition Therapy and Insulin Initiation

Start all women with GDM on Medical Nutrition Therapy (MNT) immediately at diagnosis, and add insulin only when glycemic targets are not met (fasting ≥95 mg/dL, 1-hour postprandial ≥140 mg/dL, or 2-hour postprandial ≥120 mg/dL) or when signs of excessive fetal growth appear. 1

Medical Nutrition Therapy Implementation

Initial MNT Setup

• Refer to a registered dietitian with GDM experience at the time of diagnosis to create a culturally appropriate, individualized food plan. 1

• Provide at least 175 grams of carbohydrate daily distributed across three small-to-moderate meals and two to four snacks to prevent starvation ketosis while controlling postprandial glucose. 1

• Distribute carbohydrates strategically: carbohydrate is generally less well tolerated at breakfast than at other meals, so reduce breakfast carbohydrate portions accordingly. 1

• Include an evening snack to prevent accelerated overnight ketosis. 1

Energy and Weight Management

• Provide adequate energy intake to support appropriate gestational weight gain per Institute of Medicine guidelines—never recommend weight loss during pregnancy. 1

• For overweight and obese women, implement modest energy restriction (30% reduction from estimated needs) which can improve glycemic control without causing ketonemia or ketonuria. 1

• Monitor weekly weights, daily food records, and check for ketones (urine or blood) to ensure adequate caloric intake and detect if women are undereating to avoid insulin therapy. 1

Carbohydrate Management Strategy

• Train patients in carbohydrate counting and have them maintain detailed food records with corresponding postprandial glucose values. 1

• Adjust carbohydrate amount and type based on clinical outcome measures: hunger levels, plasma glucose readings, weight gain trajectory, and ketone levels. 1

• Test postprandial glucose at 1-hour (target <140 mg/dL) or 2-hour (target <120 mg/dL) after beginning meals to guide carbohydrate adjustments. 2, 3

Physical Activity Integration

• Recommend regular physical activity as an adjunct to lower fasting and postprandial glucose concentrations and improve maternal glycemia. 1

When to Initiate Insulin

Clear Indications for Insulin

Add insulin when any of the following occur despite 1-2 weeks of optimal MNT adherence:

• Fasting glucose ≥95 mg/dL on repeated measurements 2, 3

• 1-hour postprandial glucose ≥140 mg/dL 2, 3

• 2-hour postprandial glucose ≥120 mg/dL 2, 3

• Signs of excessive fetal growth on ultrasound (elevated abdominal circumference for gestational age), regardless of glucose values 1, 3

Insulin Initiation Approach

• No specific insulin regimen has demonstrated superiority in GDM—individualize the insulin regimen to achieve glycemic targets. 1

• Typical starting approach: distribute insulin as 40% basal and 60% prandial to address the predominant postprandial hyperglycemia pattern in GDM. 4

• Once insulin is started, maintaining carbohydrate consistency at meals and snacks becomes the primary nutritional goal to match insulin dosing. 1

• Continue intensive glucose monitoring with adjustments to insulin doses based on pre-meal and postprandial readings. 1

Alternative Pharmacologic Option

• Glyburide can be considered as an alternative to insulin when insulin is not feasible, as it has minimal placental transfer (4%) and has been shown effective in one randomized controlled trial. 1

• Glyburide may be less successful in obese patients or those with marked hyperglycemia earlier in pregnancy. 1

• Balance glyburide carefully with meals and snacks to prevent maternal hypoglycemia, similar to insulin management. 1

• Metformin crosses the placenta and is not recommended for GDM treatment outside of clinical trials with long-term infant follow-up. 1

Critical Monitoring Components

• Self-monitor blood glucose at fasting and 1-2 hours postprandial to assess response to MNT and guide therapy intensification. 1, 2

• Avoid starvation ketosis by ensuring adequate caloric and carbohydrate intake—check ketones if concerns arise. 1

• Monitor fetal growth with ultrasound every 2-4 weeks starting in the second trimester to detect excessive growth requiring therapy intensification. 3

Common Pitfalls to Avoid

• Do not delay insulin initiation when glycemic targets are consistently missed—this increases risk of macrosomia and perinatal complications. 3

• Do not restrict calories excessively in an attempt to avoid insulin, as this causes ketosis which is harmful to the fetus. 1

• Do not rely on HbA1c for GDM monitoring as altered red blood cell turnover during pregnancy makes it unreliable. 2

• Do not overlook nocturnal hypoglycemia in patients with tight glucose control, especially after insulin initiation. 2