What is the recommended management for a pregnant woman diagnosed with gestational diabetes by a standard oral glucose tolerance test?

Management of Gestational Diabetes Mellitus

All women diagnosed with gestational diabetes should immediately begin medical nutrition therapy, physical activity, and daily self-monitoring of blood glucose, with insulin added as first-line pharmacologic therapy if glycemic targets are not achieved within 1-2 weeks of lifestyle intervention. 1, 2

Initial Management: Lifestyle Intervention

Medical Nutrition Therapy

• Work with a registered dietitian to develop an individualized meal plan providing minimum daily intake of 175g carbohydrate, 71g protein, and 28g fiber 1, 2
• Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats 2
• Use a low glycemic index diet to avoid postprandial hyperglycemia and reduce insulin resistance 3
• 70-85% of women achieve adequate glycemic control with lifestyle modifications alone 4, 1, 2

Physical Activity

• Aim for at least 150 minutes of moderate-intensity aerobic activity weekly, preferably spread throughout the week, or 20-50 minutes per day, 2-7 days per week if not contraindicated 1, 2

Blood Glucose Monitoring Targets

Daily self-monitoring should target: 4, 1, 2

• Fasting glucose < 95 mg/dL (5.3 mmol/L)
• 1-hour postprandial < 140 mg/dL (7.8 mmol/L) OR
• 2-hour postprandial < 120 mg/dL (6.7 mmol/L)

Monitor 4-6 times daily (fasting and postprandial values) to guide treatment decisions 1, 5

Pharmacologic Therapy: When and What to Use

Indications for Insulin Initiation

Start insulin therapy when glycemic targets are not met within 1-2 weeks of lifestyle intervention alone 4, 1, 2, 5

Specific thresholds for insulin initiation: 4

• Fasting plasma glucose ≥ 95 mg/dL despite lifestyle modification
• 1-hour postprandial ≥ 140 mg/dL despite lifestyle modification
• 2-hour postprandial ≥ 130 mg/dL despite lifestyle modification

First-Line Pharmacologic Agent: Insulin

Insulin is the preferred and recommended first-line medication for gestational diabetes because it does not cross the placenta to a measurable extent and has the most extensive safety record. 4, 1, 2, 5

Preferred Insulin Types

• Rapid-acting: Insulin lispro and insulin aspart are the preferred options, as they have been studied in randomized controlled trials and demonstrate safety in pregnancy 5
• Basal insulin: NPH insulin and insulin detemir are the preferred long-acting options 5, 6
• Insulin glargine is acceptable, particularly for women already well-controlled on this regimen pre-pregnancy, despite limited randomized trial data 5

Initial Insulin Dosing Strategy

• Calculate total daily dose as 0.5 units/kg/day based on current body weight 5
• Divide as 50% basal insulin and 50% prandial insulin distributed across three meals 5
• Both multiple daily injections and continuous subcutaneous insulin infusion are equally acceptable 5

Insulin Titration

• Adjust doses every 2-3 days by 2-4 units based on daily glucose monitoring 5
• During weeks 17-36 of gestation, insulin resistance rises exponentially, with requirements typically increasing by approximately 5% per week and potentially doubling or tripling by week 36 5
• Weekly or biweekly dose adjustments are often needed in the third trimester 1

Why NOT Metformin or Glyburide as First-Line

Metformin and glyburide should NOT be used as first-line agents for gestational diabetes. 4, 2, 5

Critical reasons: 4, 2

• Both medications cross the placenta to the fetus
• Metformin achieves fetal cord concentrations comparable to or higher than maternal levels 5
• Glyburide fails to provide adequate glycemic control in 23% of women with GDM 4, 2
• Metformin fails in 25-28% of women with GDM 4, 2
• Long-term offspring safety data are lacking or concerning 4
• Glyburide causes prolonged severe hypoglycemia (4-10 days) in neonates born to mothers receiving the drug at delivery 7

Monitoring During Treatment

Glucose Monitoring

• Perform daily self-monitoring of fasting and postprandial glucose (4-6 checks per day) 1, 5
• Postprandial monitoring is superior to preprandial monitoring for women treated with insulin 4

A1C Monitoring

• Check A1C monthly with a target < 6% (42 mmol/mol) if achievable without significant hypoglycemia 5
• If hypoglycemia risk is high, a target of < 7% (53 mmol/mol) is acceptable 5
• A1C is a secondary metric and cannot replace frequent self-monitoring, as it may miss postprandial spikes that drive fetal macrosomia 5

Fetal Surveillance

• For women requiring insulin or with poor glucose control, start fetal surveillance at 32 weeks of gestation 8
• Measure fetal abdominal circumference in early third trimester to identify risk of macrosomia 4

Critical Safety Considerations

Hypoglycemia Education

Provide comprehensive hypoglycemia education to the patient and family before initiating insulin, covering prevention, recognition (cold sweat, fatigue, nervousness, shakiness, rapid heartbeat, nausea, personality change, confusion), and treatment (immediate intake of glucose, milk, or juice) 5, 6

Red-Flag Situations

• A sudden, unexplained reduction in insulin requirements may indicate placental insufficiency and warrants immediate obstetric evaluation 5
• Diabetic ketoacidosis can develop at relatively low glucose levels (< 200 mg/dL) in pregnancy and carries high risk of stillbirth; urgent emergency care is required 5

Insulin Storage and Administration

• NPH insulin must be mixed before each injection by turning the device up and down at least 10 times until uniformly white and cloudy 6
• Never use insulin if the precipitate has become lumpy, granular, or formed solid particles 6
• Rotate injection sites (thighs, upper arms, buttocks, abdomen) about an inch apart 6
• Keep needle under skin for at least 6 seconds after injection to ensure full dose delivery 6

Postpartum Management

Immediate Postpartum

• Insulin requirements drop dramatically immediately after delivery 4, 1
• For women with gestational diabetes, stop insulin and check blood glucose before meals and 2 hours after meals for 48 hours 5
• For women with pre-existing diabetes, resume insulin at approximately 80% of pre-pregnancy doses or 50% of end-of-pregnancy doses to avoid severe hypoglycemia 5

Postpartum Screening

• Test for persistent diabetes or prediabetes at 4-12 weeks postpartum using a 75g oral glucose tolerance test with non-pregnancy diagnostic criteria 4, 1
• The OGTT is more sensitive than A1C at this timepoint because A1C may be persistently lowered by increased red blood cell turnover, blood loss at delivery, or the preceding glucose profile 4

Long-Term Follow-Up

• Women with GDM have a 50-60% lifetime risk of developing type 2 diabetes 4
• Absolute risk increases linearly: approximately 20% at 10 years, 30% at 20 years, 40% at 30 years, 50% at 40 years, and 60% at 50 years 4
• Screen for diabetes or prediabetes every 1-3 years using any recommended glycemic test (A1C, fasting plasma glucose, or OGTT) 4, 1

Risk Reduction Strategies

• Women with overweight/obesity and prediabetes should receive intensive lifestyle interventions and/or metformin to prevent progression to diabetes 4, 1
• Breastfeeding is recommended to reduce the risk of maternal type 2 diabetes 4
• Women planning future pregnancies should seek preconception screening for diabetes and preconception care to identify and treat hyperglycemia 4, 1

Multidisciplinary Care

Referral to a specialized diabetes-and-pregnancy center with team-based care (maternal-fetal medicine, endocrinology, diabetes education, nutrition) is strongly recommended for optimal maternal and fetal outcomes, particularly for women requiring insulin 1, 5