What is the initial management for a pregnant woman newly diagnosed with diabetes mellitus?

Initial Management of Newly Diagnosed Diabetes in Pregnancy

Begin immediately with medical nutrition therapy (MNT) and self-monitoring of blood glucose (SMBG), 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, 2

Step 1: Immediate Lifestyle Intervention

Medical Nutrition Therapy

• Refer to a registered dietitian familiar with diabetes in pregnancy management within the first week of diagnosis to develop an individualized nutrition plan 2
• Prescribe a diet providing minimum 175 g carbohydrate daily, 71 g protein daily, and 28 g fiber daily 2, 3
• Never reduce carbohydrates below 175 g/day, as this risks fetal growth compromise and maternal ketosis 3
• Distribute carbohydrates across 3 small-to-moderate meals and 2-4 snacks throughout the day, with an evening snack usually necessary to prevent accelerated ketosis overnight 2, 3
• Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats 2, 3

Physical Activity

• Prescribe at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week 2
• Regular aerobic exercise lowers fasting and postprandial glucose and should be used as an adjunct to nutrition therapy 3

Step 2: Blood Glucose Monitoring Protocol

Daily Monitoring Schedule

• Check fasting glucose daily upon waking 1, 2
• Check postprandial glucose after each main meal (breakfast, lunch, dinner) 1, 2
• Choose either 1-hour postprandial OR 2-hour postprandial measurements consistently 2

Glycemic Targets

• Fasting glucose: 70-95 mg/dL (3.9-5.3 mmol/L) 1, 2
• 1-hour postprandial: 110-140 mg/dL (6.1-7.8 mmol/L) 1, 2
• 2-hour postprandial: 100-120 mg/dL (5.6-6.7 mmol/L) 1, 2

A1C Monitoring

• Target A1C < 6% (42 mmol/mol) if achievable without significant hypoglycemia 1
• Use A1C as a secondary measure only, not as a replacement for SMBG, because it may not capture postprandial hyperglycemia that drives macrosomia 1, 2

Step 3: Pharmacologic Therapy Decision Point

When to Initiate Insulin

• If glycemic targets are not achieved within 1-2 weeks of MNT alone, initiate insulin therapy 1, 2
• Insulin is the preferred and recommended first-line pharmacologic agent because it does not cross the placenta to a measurable extent 2
• Insulin has unlimited dose-titration capacity, allowing achievement of target glucose levels without a ceiling effect 2

Insulin Dosing Principles

• Insulin requirements increase linearly around 16 weeks gestation, approximately 5% per week through week 36, usually resulting in a doubling of daily insulin dose compared to prepregnancy requirements 1
• Use a smaller proportion of total daily dose as basal insulin and a greater proportion as prandial insulin to match the physiologic needs of pregnancy 2
• Frequent titration is required to match changing requirements throughout pregnancy 4

Oral Agents: When NOT to Use

• Avoid metformin and glyburide as first-line therapy due to inferior outcomes and safety profiles compared to insulin 2
• Metformin crosses the placenta, producing umbilical-cord concentrations equal to or higher than maternal levels, and children exposed in utero had higher BMI and waist circumference at age 9 years 2
• Glyburide crosses the placenta (fetal cord concentrations 50-70% of maternal levels) and is associated with higher rates of neonatal hypoglycemia, macrosomia, and increased fetal abdominal circumference 2
• Approximately 25-28% of women fail to achieve glycemic targets with metformin alone, and 23% fail with glyburide 2

Oral Agents: Limited Exceptions

• Oral agents may be considered only when insulin administration is impractical or unsafe due to cost, language barriers, limited health literacy, or cultural factors 2
• If an oral agent is chosen, metformin is preferred over glyburide because it is linked to lower incidences of neonatal hypoglycemia and macrosomia 2
• Patients must be counseled that all oral agents cross the placenta and long-term offspring safety data are lacking 2

Step 4: Additional Maternal and Fetal Surveillance

Maternal Monitoring

• Measure blood pressure and urinary protein at each prenatal visit to detect preeclampsia, as the risk of hypertensive disorders is increased 2
• Prescribe low-dose aspirin 60-150 mg/day (usual dose 81 mg/day) from the end of the first trimester until delivery to lower the risk of preeclampsia 1

Fetal Monitoring

• Begin ultrasound monitoring of fetal abdominal circumference in the second and early third trimesters, repeated every 2-4 weeks 2
• Consider lower glycemic targets or intensification of pharmacologic therapy when fetal abdominal circumference is excessive (≥75th percentile) 2
• Teach mothers to monitor fetal movements during the last 8-10 weeks of pregnancy and report immediately any reduction 2

Step 5: Continuous Glucose Monitoring Consideration

• Continuous glucose monitoring (CGM) in pregnant women with type 1 diabetes has been shown to improve neonatal outcomes in randomized controlled trials 1
• CGM may be useful for women with type 2 diabetes or those requiring intensive insulin therapy, though evidence is strongest for type 1 diabetes 1

Common Pitfalls to Avoid

• Do not delay insulin initiation beyond 1-2 weeks if lifestyle modifications fail to achieve targets, as this increases risk of macrosomia and other complications 2
• Do not start oral agents before attempting insulin in newly diagnosed diabetes in pregnancy, as the safety concerns of placental transfer outweigh convenience 2
• Do not use hypocaloric diets <1,200 kcal/day, which cause ketonemia 3
• Do not rely on A1C alone for glycemic assessment, as it may miss postprandial hyperglycemia 1, 2
• Discontinue metformin immediately if the patient develops hypertension, preeclampsia, or any sign of placental insufficiency, to prevent fetal growth restriction or acidosis 2

Postpartum Follow-Up

• Test 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 A1C at this visit because the concentration may still be influenced by changes during pregnancy and/or peripartum blood loss 2
• Women with a history of gestational diabetes have a 50-70% risk of developing type 2 diabetes over 15-25 years, requiring lifelong screening for diabetes at least every 3 years 2