What are the management options for Gestational Diabetes Mellitus (GDM)?

Management of Gestational Diabetes Mellitus

Lifestyle modification through medical nutrition therapy and exercise is the first-line treatment for GDM and successfully controls glucose in 70-85% of women; when pharmacological therapy is needed, insulin is the preferred agent because it does not cross the placenta. 1

Glycemic Targets

Aim for the following blood glucose goals 1:

• Fasting glucose <95 mg/dL
• One-hour postprandial glucose <140 mg/dL
• Two-hour postprandial glucose <120 mg/dL

Self-monitoring of blood glucose is essential to assess whether these targets are being met 1.

First-Line: Lifestyle Modifications

Medical Nutrition Therapy (MNT)

Work with a registered dietitian experienced in GDM management to develop a meal plan that achieves glycemic targets while supporting appropriate gestational weight gain 1.

Specific dietary requirements include 1:

• Minimum 175g carbohydrate daily
• Minimum 71g protein daily
• 28g fiber daily
• Emphasize monounsaturated and polyunsaturated fats
• Limit saturated fats and avoid trans fats

The focus should be on carbohydrate type, amount, and distribution throughout the day since carbohydrate intake directly affects postprandial glucose excursions 2. A low glycemic index diet with calorie restriction helps avoid postprandial hyperglycemia and reduces insulin resistance 3.

Physical Activity

Exercise has beneficial effects on glucose and insulin levels and contributes to better glycemic control 2. Regular physical activity is an essential adjunct to dietary modifications 4.

Second-Line: Pharmacological Therapy

When to Initiate Medication

Start pharmacological therapy when lifestyle modifications fail to achieve glycemic targets during follow-up visits 3.

Insulin: Preferred First-Line Agent

Insulin is the preferred medication for GDM because it does not cross the placenta to a measurable extent 1, 5.

Insulin options include 6:

• Rapid-acting analogues (aspart, lispro): Achieve postprandial targets with less hypoglycemia compared to regular insulin
• Long-acting analogues (glargine, detemir): Safe with similar maternal/fetal outcomes compared to NPH insulin

Dosage adjustments may be necessary if patients change physical activity or meal plans 5. When switching from other intermediate or long-acting insulin preparations to insulin detemir, dosages can be prescribed unit-to-unit, but timing and dose may need adjustment to reduce hypoglycemia risk 5.

Oral Antihyperglycemic Agents: Not First-Line

Metformin and glyburide should not be used as first-line agents because both cross the placenta 1.

Metformin 6:

• Has good efficacy and short-term safety data
• Freely crosses the placenta
• Long-term safety data are lacking
• Up to 46% of women may require additional insulin to maintain glucose targets 3

Glyburide 1, 6:

• Has minimal placental transfer but still crosses
• Associated with increased neonatal hypoglycemia and macrosomia compared to insulin
• May increase rates of large-for-gestational-age infants

Monitoring During Pregnancy

• Monitor blood glucose levels, HbA1c, and ketonuria to analyze efficacy of management 3
• Check blood pressure and urinary protein at each prenatal visit, as women with GDM have increased risk of hypertensive disorders 1
• For patients requiring medications or with poor glucose control, begin fetal surveillance at 32 weeks gestation 7
• Telehealth visits improve outcomes compared to standard in-person care 1

Delivery Planning

For diet-controlled GDM: Delivery at 39/0 to 40/6 weeks gestation 7

For medication-controlled GDM: Delivery at 39/0 to 39/6 weeks gestation 7

Assess for fetal macrosomia (estimated fetal weight >4,000g) and discuss risks/benefits of prelabor cesarean delivery if estimated fetal weight exceeds 4,500g 7.

Critical Pitfalls to Avoid

• Do not prematurely initiate pharmacological therapy: 70-85% of women achieve control with lifestyle modification alone 1
• Do not assume oral agents are equivalent to insulin: They cross the placenta and have less robust safety data 1, 6
• Do not mix insulin detemir with other insulin preparations: This can alter the action profile and reduce efficacy by up to 40% 5
• Do not overlook dose adjustments: Insulin requirements may change with renal or hepatic impairment, intercurrent illness, emotional stress, or changes in physical activity 5