What is the recommended management for a pregnant woman diagnosed with gestational diabetes mellitus?

Management of Gestational Diabetes Mellitus

Begin immediately with medical nutrition therapy and self-monitoring of blood glucose upon diagnosis, targeting fasting glucose <95 mg/dL, 1-hour postprandial <140 mg/dL, or 2-hour postprandial <120 mg/dL; if these targets are not achieved within 1–2 weeks with lifestyle modifications alone, initiate insulin therapy as the first-line pharmacologic agent. 1

Initial Management Framework

Immediate Actions at Diagnosis

• Refer the patient to a registered dietitian nutritionist familiar with GDM management within the first week of diagnosis to develop an individualized nutrition plan. 1, 2
• Initiate 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

Expected Outcomes with Lifestyle Modification

• Between 70–85% of women diagnosed with GDM can achieve adequate glycemic control with lifestyle measures alone, eliminating the need for medication in the majority of cases. 1, 3
• This high success rate underscores the importance of giving lifestyle interventions an adequate trial before escalating to pharmacologic therapy. 1

Medical Nutrition Therapy Specifics

Mandatory Macronutrient Minimums

• Carbohydrate: minimum 175 g daily (approximately 35% of a 2,000-calorie diet), distributed across 3 small-to-moderate meals and 2–4 snacks throughout the day. 1, 2
• Protein: minimum 71 g daily to support maternal and fetal needs. 1, 2
• Fiber: minimum 28 g daily to improve glycemic stability. 1, 2
• An evening snack is usually necessary to prevent accelerated ketosis overnight. 1

Critical Dietary Composition

• Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats entirely. 1, 2
• Focus on nutrient-dense, whole foods including fruits, vegetables, legumes, and whole grains; limit simple carbohydrates, processed foods, fatty red meat, and sweetened foods and beverages. 2
• Do NOT reduce carbohydrates below 175 g/day, as intakes below this threshold may compromise fetal growth when total energy intake is inadequate. 1, 2
• Substituting excessive fat for carbohydrate can increase maternal lipolysis, raise free-fatty-acid levels, and worsen insulin resistance. 1, 2

Caloric Targets

• For overweight women, caloric needs are approximately 30–32 kcal/kg of pre-pregnancy body weight, plus an additional 340 kcal/day in the second trimester, typically totaling 2,000–2,200 kcal/day. 1
• Hypocaloric diets <1,200 kcal/day cause ketonemia and are contraindicated. 2
• Extreme dietary patterns such as ketogenic diet, Paleo diet, and diets characterized by excess saturated fats should be avoided. 2

Blood Glucose Monitoring Strategy

Daily Self-Monitoring Protocol

• Check fasting glucose daily upon waking. 1
• Check postprandial glucose after each main meal—choose either 1-hour postprandial or 2-hour postprandial measurements consistently. 1
• Postprandial monitoring is superior to preprandial monitoring alone and is associated with better glycemic control and lower risk of preeclampsia. 1

Glycemic Targets

• Fasting glucose: <95 mg/dL 1, 3, 2
• 1-hour postprandial: <140 mg/dL 1, 3, 2
• 2-hour postprandial: <120 mg/dL 1, 3, 2

HbA1c Monitoring

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

Ketone Monitoring

• Urine ketone testing may help detect inadequate caloric or carbohydrate intake in women on calorie-restricted diets. 1
• Finger-stick blood ketone measurement correlates more closely with laboratory β-hydroxybutyrate levels than urine ketones. 1

Pharmacologic Management Algorithm

When to Initiate Insulin

• Start insulin immediately if glycemic targets are not met within 1–2 weeks of lifestyle modifications alone. 1, 3
• Insulin should also be started immediately when any of the following are present on initial assessment: fasting glucose ≥95 mg/dL, 1-hour postprandial ≥140 mg/dL, or 2-hour postprandial ≥120 mg/dL. 1

Why Insulin is First-Line

• Insulin is the preferred and recommended first-line pharmacologic agent because it does not cross the placenta to a measurable extent. 1, 3
• Insulin has unlimited dose-titration capacity, allowing clinicians to achieve target glucose levels without a ceiling effect. 1
• Insulin requirements rise linearly by approximately 5% each week from diagnosis through week 36 of gestation, often resulting in a doubling of the pre-pregnancy dose by late pregnancy; frequent titration is required to match this increase. 1

Insulin Dosing

• The initial total daily insulin dose is 0.7–1.0 units/kg of maternal weight, allocated as approximately 40% basal and 60% prandial insulin. 1
• A smaller proportion of total daily dose is given as basal insulin and a greater proportion as prandial insulin compared to non-pregnant dosing. 1

Why Oral Agents Are NOT First-Line

Metformin

• Metformin is NOT recommended as first-line therapy because it crosses the placenta, producing umbilical-cord concentrations equal to or higher than maternal levels. 1, 3
• The MiG-TOFU follow-up study showed that children aged 9 years exposed in utero to metformin had higher body-mass index, waist-to-height ratio, and waist circumference compared with those exposed to insulin, indicating potential long-term metabolic effects. 1
• Approximately 25–28% of women fail to achieve glycemic targets when treated with metformin alone, necessitating additional therapy. 1, 3
• Metformin should be avoided in women who develop hypertension, preeclampsia, or any condition predisposing to intrauterine growth restriction, because of the risk of fetal growth restriction or metabolic acidosis. 1

Glyburide

• Glyburide is NOT recommended as first-line therapy because it crosses the placenta, with fetal cord concentrations reaching 50–70% of maternal levels. 1, 3
• Meta-analyses demonstrate that glyburide use is associated with higher rates of neonatal hypoglycemia, macrosomia, and increased fetal abdominal circumference compared with insulin or metformin. 1, 3
• Glyburide failed to meet non-inferiority criteria versus insulin for a composite neonatal outcome (hypoglycemia, macrosomia, hyperbilirubinemia). 1
• About 23% of women on glyburide do not reach glycemic targets. 1, 3
• No long-term safety data exist for offspring exposed to glyburide. 1

When Oral Agents May Be Considered

• Oral agents can be used when insulin administration is impractical or unsafe because of cost, language barriers, limited health literacy, or cultural factors. 1
• If a well-informed patient declines insulin after comprehensive counseling, an oral agent may be offered as an alternative. 1
• When an oral agent is chosen, metformin is preferred over glyburide because it is linked to lower incidences of neonatal hypoglycemia and macrosomia. 1
• Patients must be counseled that all oral agents cross the placenta and that long-term offspring safety data are lacking. 1
• If glycemic targets are not met within 1–2 weeks of oral therapy, transition promptly to insulin or add insulin to the regimen. 1

Fetal Surveillance

Ultrasound Monitoring

• Serial ultrasound measurement of fetal abdominal circumference should begin in the second and early third trimesters and be repeated every 2–4 weeks. 1
• When fetal abdominal circumference is <75th percentile (normal growth), a less intensified management approach may be adopted, but self-monitoring of blood glucose should continue. 1
• When fetal abdominal circumference is ≥75th percentile (excessive growth), lower targets for glycemic control or intensification of pharmacologic therapy should be considered. 1

Fetal Movement Monitoring

• Teach mothers to monitor fetal movements during the last 8–10 weeks of pregnancy and report immediately any reduction. 1
• Women whose fasting glucose exceeds 105 mg/dL or who progress beyond term require heightened surveillance for fetal demise. 1

Maternal Surveillance

• Measure blood pressure and urinary protein at each prenatal visit to detect preeclampsia, as women with GDM have a 1.6-fold higher risk of developing preeclampsia compared with non-diabetic pregnancies. 1

Intrapartum Management

• Monitor maternal blood glucose during labor every 1–2 hours, targeting a range of 80–110 mg/dL to reduce the risk of fetal hypoxia and neonatal hypoglycemia. 1
• If capillary glucose exceeds 180 mg/dL (10 mmol/L) during labor, administer an insulin bolus. 1
• If glucose exceeds 297 mg/dL (16.5 mmol/L), delay non-urgent procedures and give corrective insulin. 1

Delivery Timing

• For women with diet-controlled GDM meeting glycemic targets, delivery at 39–40 weeks of gestation is appropriate. 1
• For women requiring insulin or with poor glycemic control, delivery at 39 weeks of gestation (39⁰–39⁶ weeks) is recommended to balance maternal and fetal outcomes. 1
• Postponing delivery beyond 40 weeks in women requiring insulin increases perinatal mortality. 1

Postpartum Follow-Up

Immediate Postpartum (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
• 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
• 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

Breastfeeding

• Strongly encourage breastfeeding because it provides immediate nutritional and immunologic benefits and may confer longer-term metabolic advantages for both mother and child. 1

Telehealth Considerations

• A meta-analysis of 32 randomized controlled trials demonstrated that telehealth visits for GDM reduce incidences of cesarean delivery, neonatal hypoglycemia, premature rupture of membranes, macrosomia, pregnancy-induced hypertension or preeclampsia, preterm birth, neonatal asphyxia, and polyhydramnios compared with standard in-person care. 1

Common Pitfalls to Avoid

• Do NOT start oral agents before attempting insulin, as the safety concerns of placental transfer outweigh convenience. 1
• Do NOT reduce carbohydrates below 175 g/day, as this risks fetal growth compromise and maternal ketosis. 1, 2
• Do NOT delay insulin initiation if glycemic targets are not met within 1–2 weeks of lifestyle modifications. 1, 3
• Discontinue metformin immediately and switch to insulin if the patient develops hypertension, preeclampsia, or any sign of placental insufficiency. 1
• Recognize that glyburide carries the poorest safety profile among available agents, with the highest rates of neonatal hypoglycemia and macrosomia. 1