What is the recommended management of gestational diabetes, including diagnosis, lifestyle therapy, glucose targets, pharmacologic treatment, delivery planning, and postpartum follow‑up?

Management of Gestational Diabetes Mellitus

Diagnosis

Gestational diabetes mellitus (GDM) is diagnosed using either a one-step 75-g oral glucose tolerance test (OGTT) or a two-step approach, with only one abnormal value required for diagnosis in the one-step method. 1

Screening Strategy

• Screen all pregnant women at 24-28 weeks' gestation using either the one-step or two-step approach 2, 1
• For women with risk factors (prior GDM, obesity, family history of diabetes, previous macrosomic infant), perform early screening at the first prenatal visit using fasting plasma glucose, HbA1c, or random glucose 2
• If early screening is negative in high-risk women, repeat screening at 24-28 weeks 2, 1

Diagnostic Thresholds (One-Step 75-g OGTT)

• Fasting ≥92 mg/dL (5.1 mmol/L) 2, 1
• 1-hour ≥180 mg/dL (10.0 mmol/L) 1
• 2-hour ≥153 mg/dL (8.5 mmol/L) 2, 1

Early Pregnancy Overt Diabetes Criteria

• Fasting plasma glucose ≥126 mg/dL (7.0 mmol/L) 2
• Random glucose ≥200 mg/dL (11.1 mmol/L) 2
• HbA1c ≥6.5% 2
• If overt diabetes is detected, manage as preexisting diabetes, not GDM 2

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Lifestyle Therapy

Medical nutrition therapy (MNT) and physical activity are the essential first-line interventions for all women with GDM and must be initiated immediately upon diagnosis. 1

Medical Nutrition Therapy

• Refer to a registered dietitian within the first week of diagnosis 1
• Prescribe minimum 175 g carbohydrate daily, 71 g protein daily, and 28 g fiber daily 1
• Distribute carbohydrates across 3 small-to-moderate meals and 2-4 snacks throughout the day, with an evening snack to prevent accelerated overnight ketosis 1
• Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats 1
• Never reduce carbohydrates below 175 g/day, as this may compromise fetal growth 1
• For overweight women, prescribe approximately 2,000-2,200 kcal/day based on pre-pregnancy BMI 1

Physical Activity

• Prescribe at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week 1

Expected Outcomes

• 70-85% of women with GDM achieve adequate glycemic control with lifestyle modifications alone 1

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Glucose Targets and Monitoring

Target fasting glucose <95 mg/dL, 1-hour postprandial <140 mg/dL, or 2-hour postprandial <120 mg/dL. 1

Self-Monitoring Protocol

• Check fasting glucose daily upon waking 1
• Check postprandial glucose after each main meal (breakfast, lunch, dinner) 1
• Choose either 1-hour OR 2-hour postprandial measurements consistently—do not alternate 1
• Postprandial monitoring is superior to preprandial monitoring and reduces preeclampsia risk 1

HbA1c Monitoring

• HbA1c has limited utility in GDM management and should NOT replace blood glucose monitoring 1
• If used, measure monthly with target <6% (42 mmol/mol) if achievable without hypoglycemia 1
• HbA1c does not adequately detect postprandial hyperglycemia, which drives macrosomia 1

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Pharmacologic Treatment

Insulin is the preferred and recommended first-line pharmacologic agent when glycemic targets are not achieved within 1-2 weeks of lifestyle modifications. 1

Insulin Therapy

• Initiate insulin if targets are not met within 1-2 weeks of MNT and exercise 1
• Insulin does not cross the placenta in measurable amounts and has the most extensive safety record 1
• Insulin allows unlimited dose titration without a ceiling effect 1
• Insulin requirements increase throughout pregnancy and require frequent adjustment 1
• Insulin requirements drop dramatically immediately postpartum, often to roughly half of prepregnancy requirements 2

Oral Agents: When to Consider

• Metformin and glyburide are NOT recommended as first-line therapy 1
• Consider oral agents only when insulin is impractical or unsafe due to cost, language barriers, limited health literacy, or cultural factors 1
• If oral agents are used, metformin is preferred over glyburide due to lower rates of neonatal hypoglycemia and macrosomia 1

Metformin: Specific Concerns

• Metformin crosses the placenta, producing umbilical-cord concentrations equal to or higher than maternal levels 1
• Children exposed to metformin in utero have higher BMI, waist-to-height ratio, and waist circumference at age 9 years compared to insulin-exposed children 1
• 25-28% of women fail to achieve glycemic targets with metformin alone 1
• Avoid metformin in women with hypertension, preeclampsia, or conditions predisposing to intrauterine growth restriction 1

Glyburide: Specific Concerns

• Glyburide crosses the placenta, with fetal cord concentrations reaching 50-70% of maternal levels 1
• Glyburide is associated with higher rates of neonatal hypoglycemia, macrosomia, and increased fetal abdominal circumference compared to insulin 1
• Glyburide failed non-inferiority criteria versus insulin for composite neonatal outcomes 1
• 23% of women on glyburide do not reach glycemic targets 1
• No long-term offspring safety data exist 1

Critical Action Points

• If glycemic targets are not met within 1-2 weeks of oral therapy, transition promptly to insulin or add insulin 1
• Discontinue metformin immediately and switch to insulin if hypertension, preeclampsia, or placental insufficiency develops 1
• Counsel all patients that oral agents cross the placenta and long-term offspring safety data are lacking 1

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Fetal and Maternal Surveillance

Fetal Monitoring

• Begin ultrasound monitoring of fetal abdominal circumference in the second and early third trimesters, repeating every 2-4 weeks 1
• For women requiring medications, initiate antepartum fetal surveillance starting at 32 weeks' gestation 3, 4
• Consider lower glycemic targets or intensified therapy when fetal abdominal circumference is >75th percentile 1
• Teach mothers to monitor fetal movements during the last 8-10 weeks and report any reduction immediately 1

Maternal Monitoring

• Measure blood pressure and urinary protein at each prenatal visit to detect preeclampsia 1
• Women with type 1 or type 2 diabetes should receive low-dose aspirin 60-150 mg/day (usual dose 81 mg/day) from the end of the first trimester until delivery to reduce preeclampsia risk 2

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Delivery Planning

Delivery timing depends on glycemic control and medication requirements. 1

Diet-Controlled GDM

• Deliver at 39 0/7 to 40 6/7 weeks' gestation for women with diet-controlled GDM meeting glycemic targets 1, 3

Medication-Controlled GDM

• Deliver at 39 0/7 to 39 6/7 weeks' gestation for women requiring insulin or with poor glycemic control 1, 3, 4

Macrosomia Considerations

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

Intrapartum Glucose Management

• Insulin resistance decreases dramatically immediately postpartum 2
• Decreased glucose testing and sliding-scale insulin dosing can safely replace continuous intravenous insulin drips during labor 4

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Postpartum Follow-Up

All women with GDM must be tested for persistent diabetes or prediabetes at 4-12 weeks postpartum using a 75-g OGTT with non-pregnancy diagnostic criteria. 2, 1, 5

Immediate Postpartum Testing (4-12 Weeks)

• Use the 75-g OGTT, NOT HbA1c, for postpartum screening 5
• HbA1c is unreliable due to increased red blood cell turnover during pregnancy, blood loss at delivery, and the preceding 3-month glucose profile 5
• Diabetes is diagnosed when fasting plasma glucose ≥126 mg/dL or 2-hour plasma glucose ≥200 mg/dL 5
• If both fasting and 2-hour glucose are abnormal on a single test, diabetes is confirmed without repeat testing 5
• In the absence of unequivocal hyperglycemia, two abnormal values are required for diagnosis 2

Management of Prediabetes

• Women with prediabetes should receive intensive lifestyle interventions and/or metformin to prevent diabetes 2, 5
• Lifestyle intervention reduces progression to diabetes by 35% over 10 years 2
• Metformin reduces progression to diabetes by 40% over 10 years 2, 5
• Number needed to treat is 5-6 patients over 3 years for both interventions 5

Lifelong Screening

• Women with a history of GDM should have lifelong screening for type 2 diabetes or prediabetes every 1-3 years 2, 5
• Women with prior GDM have a 50-70% lifetime risk of developing type 2 diabetes 1, 5
• Use standard non-pregnant criteria: annual HbA1c, annual fasting plasma glucose, or triennial 75-g OGTT 1

Additional Postpartum Care

• Discuss and implement a contraceptive plan with all women of reproductive potential 2
• Breastfeeding is recommended to reduce the risk of maternal type 2 diabetes 2
• Women with a history of GDM should seek preconception screening for diabetes before subsequent pregnancies 2, 5
• Postpartum care should include psychosocial assessment and support for self-care 2

Critical Pitfalls to Avoid

• Do NOT test immediately postpartum while hospitalized, as this has reduced sensitivity for detecting glucose intolerance 5
• Do NOT use HbA1c for the 4-12 week postpartum screening, as it will miss cases 5
• Do NOT delay postpartum testing beyond 12 weeks, as engagement decreases significantly 2