What is the best management approach for a pregnant woman with gestational diabetes mellitus (GDM)?

Management of Gestational Diabetes Mellitus

Begin immediately with medical nutrition therapy (MNT) and self-monitoring of blood glucose upon diagnosis, and if glycemic targets are not achieved within 1-2 weeks of lifestyle modifications alone, initiate insulin therapy as the first-line pharmacologic agent. 1

Initial Management Steps

Immediate Actions After Diagnosis

• Refer to a registered dietitian familiar with GDM management within the first week of diagnosis to develop a nutrition plan 1
• Start daily self-monitoring of blood glucose: check fasting glucose upon waking and postprandial glucose after each main meal (breakfast, lunch, dinner) 1
• Prescribe at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week 1

Glycemic Targets to Achieve

• Fasting glucose <95 mg/dL 1, 2
• 1-hour postprandial <140 mg/dL 1, 2
• 2-hour postprandial <120 mg/dL 1, 2
• Choose either 1-hour OR 2-hour postprandial measurements consistently 1

Lifestyle Modifications (First-Line Treatment)

Medical Nutrition Therapy Requirements

Mandatory minimum daily requirements for all pregnant women with GDM: 1

• Minimum 175g carbohydrate daily 1, 3
• Minimum 71g protein daily 1, 3
• 28g fiber daily 1, 3
• Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats 1, 3

Critical caveat: Do NOT reduce carbohydrates below 175g/day, as intakes below this threshold may compromise fetal growth when total energy intake is inadequate 1

Caloric Intake Guidelines

• For overweight women: approximately 30-32 kcal/kg of pre-pregnancy body weight, plus an additional 340 kcal/day in the second trimester 1
• Typical range: approximately 2,000-2,200 kcal/day for overweight pregnant women with GDM 1

Physical Activity Prescription

• At least 150 minutes of moderate-intensity aerobic activity weekly 1
• Resistance, aerobic exercise, or a combination of both are effective for glucose control 4
• Exercise for at least 20-50 minutes a minimum of 2 times per week at moderate intensity 4

Pharmacologic Management (Second-Line Treatment)

When to Initiate Medication

Initiate insulin therapy if glycemic targets are not achieved within 1-2 weeks of lifestyle modifications alone 1, 2

Before declaring treatment failure, verify adequate lifestyle modifications including consultation with a registered dietitian, minimum dietary requirements, and physical activity 2

Insulin as First-Line Pharmacologic Agent

Insulin is the preferred and recommended first-line pharmacologic agent because it does not cross the placenta to a measurable extent 1, 2, 3

Key insulin prescribing principles: 2

• Smaller proportion as basal insulin
• Greater proportion as prandial insulin
• Frequent titration required throughout pregnancy

Oral Agents: Not Recommended First-Line

• The Endocrine Society recommends avoiding metformin and glyburide as first-line therapy due to their inferior outcomes and safety profiles compared to insulin 1
• Both metformin and glyburide cross the placenta 3
• Glyburide has been associated with increased neonatal hypoglycemia and macrosomia compared to insulin 3
• Metformin may be considered when insulin cannot be prescribed, but up to 46% of women may require additional insulin to maintain expected blood glucose levels 5

Monitoring During Pregnancy

Maternal Glucose Monitoring

• Daily fasting glucose upon waking 1
• Postprandial glucose after each main meal 1
• Postprandial monitoring is superior to preprandial monitoring alone and is associated with better glycemic control and lower risk of preeclampsia 1

HbA1c Monitoring

• HbA1c has limited utility in GDM management but should be measured monthly if used, with a target HbA1c <6% (42 mmol/mol) if achievable without significant hypoglycemia 1
• HbA1c should NOT replace blood glucose monitoring because macrosomia results primarily from postprandial hyperglycemia, which HbA1c may not adequately detect 1

Fetal Surveillance

• Begin ultrasound monitoring of fetal abdominal circumference in the second and early third trimesters and repeat every 2-4 weeks 1
• Less intensified management is allowed with normal growth (fetal abdominal circumference <75th percentile for gestational age) 1
• Consider lower glycemic targets or intensification of pharmacologic therapy when fetal abdominal circumference is excessive 1
• For patients requiring medications, fetal surveillance is suggested starting at 32 weeks of gestation 6

Additional Maternal Surveillance

• Measure blood pressure and urinary protein at each prenatal visit to detect preeclampsia, as the risk of hypertensive disorders is increased in women with GDM 1
• Teach mothers to monitor fetal movements during the last 8-10 weeks of pregnancy and report immediately any reduction 1

Delivery Timing

Diet-Controlled GDM

• Delivery at 39-40 weeks of gestation is appropriate for women with diet-controlled GDM meeting glycemic targets 1

Insulin-Requiring or Poor Glycemic Control

• Delivery at 39 weeks of gestation is recommended for women requiring insulin or with poor glycemic control 1

Macrosomia Considerations

• Assess for fetal macrosomia (estimated fetal weight >4,000 g) 6
• Discuss risks and benefits of prelabor cesarean delivery if estimated fetal weight is >4,500 g 6

Postpartum Management

Immediate Postpartum Testing (4-12 Weeks)

All women with GDM must be tested for persistent diabetes or prediabetes at 4-12 weeks postpartum using a 75-g oral glucose tolerance test (OGTT) with non-pregnancy diagnostic criteria 1, 2

• Do NOT use HbA1c at this visit because the concentration may still be influenced by changes during pregnancy and/or peripartum blood loss 1

Long-Term Surveillance

• Women with a history of GDM have a 50-70% risk of developing type 2 diabetes over 15-25 years 1, 2
• Perform lifelong screening for diabetes at least every 3 years using standard non-pregnant criteria (annual HbA1c, annual fasting plasma glucose, or triennial 75-g OGTT) 1
• Continued lifestyle modifications, breastfeeding, and use of metformin can reduce the risk of developing overt diabetes 6

Common Pitfalls to Avoid

Premature Medication Escalation

• Remember that 70-85% of women can achieve glycemic targets with lifestyle modifications alone 2, 3
• Verify adequate lifestyle modifications before declaring treatment failure 2

Inadequate Monitoring

• Insulin requirements change dramatically throughout pregnancy, requiring frequent dose adjustments 2
• Inadequate monitoring frequency can lead to inadequate glycemic control 2

Using Oral Agents as First-Line

• Oral agents have inferior safety profiles compared to insulin 2
• Both metformin and glyburide cross the placenta 3

Forgetting Postpartum Follow-Up

• Women with GDM history have 50-70% risk of developing type 2 diabetes over 15-25 years 2
• Postpartum OGTT at 4-12 weeks is mandatory 1, 2

Alternative Care Delivery

• Telehealth visits for GDM patients can improve outcomes compared with standard in-person care, reducing cesarean delivery, neonatal hypoglycemia, and other complications 2, 3