How should I manage a pregnant woman in her second trimester who has just been diagnosed with diabetes?

Management of Newly Diagnosed Diabetes in the Second Trimester

Immediately initiate medical nutrition therapy with a registered dietitian and begin daily blood glucose monitoring, targeting fasting glucose <95 mg/dL and postprandial glucose <140 mg/dL (1-hour) or <120 mg/dL (2-hour); if these targets are not achieved within 1-2 weeks, start insulin therapy as the first-line pharmacologic agent. 1, 2

Immediate Initial Steps

Confirm Diagnosis Type

• Recognize that diabetes diagnosed in the second trimester may represent either gestational diabetes mellitus (GDM) or previously undiagnosed preexisting type 2 diabetes 1
• The distinction matters because preexisting diabetes carries higher risks for maternal hypertension, preeclampsia, and third-trimester pregnancy loss compared to GDM 1

Establish Baseline Glycemic Control

• Obtain fasting and postprandial glucose values immediately to assess current control and guide treatment intensity 2
• Check A1C if not recently done, though it has limited utility for ongoing GDM management; target A1C <6% (42 mmol/mol) if achievable without significant hypoglycemia 1

Initiate Aspirin Prophylaxis

• Prescribe low-dose aspirin 100-150 mg daily (162 mg is acceptable in the U.S., typically given as two 81-mg tablets) starting immediately, as you are already at 12-16 weeks or beyond 1
• This reduces preeclampsia risk, which is elevated in all forms of diabetes in pregnancy 1

Medical Nutrition Therapy (First-Line Treatment)

Urgent Dietitian Referral

• Refer to a registered dietitian nutritionist within 1 week of diagnosis 3, 2
• The dietitian will establish an individualized food plan, insulin-to-carbohydrate ratios (if insulin becomes necessary), and weight gain goals 1, 3

Specific Dietary Requirements

• Minimum 175 g carbohydrate daily (approximately 35% of a 2,000-calorie diet) 1, 3, 2
• Minimum 71 g protein daily 3, 2
• Minimum 28 g fiber daily 3, 2
• Distribute carbohydrates across 3 small-to-moderate meals and 2-4 snacks throughout the day 2
• Include an evening snack to prevent overnight hypoglycemia and accelerated ketosis 3, 2
• Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats entirely 3, 2

Weight Gain Targets

• For overweight women (BMI 25-29.9): 15-25 pounds total 1
• For obese women (BMI ≥30): 10-20 pounds total 1

Physical Activity

• Prescribe at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week 2
• Regular moderate physical activity (20-50 minutes per day, 2-7 days per week) as tolerated 3

Blood Glucose Monitoring Protocol

Daily Self-Monitoring Requirements

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

Glycemic Targets

• Fasting: <95 mg/dL (5.3 mmol/L) 1, 3, 2
• 1-hour postprandial: <140 mg/dL (7.8 mmol/L) 1, 3, 2
• 2-hour postprandial: <120 mg/dL (6.7 mmol/L) 1, 3, 2

Additional Monitoring

• Postprandial monitoring is superior to preprandial monitoring alone and is associated with better glycemic control and lower risk of preeclampsia 1, 2
• Consider continuous glucose monitoring (CGM) as an adjunct to self-monitoring, though it should not replace pre- and postprandial testing 1

When to Initiate Insulin Therapy

Timing Decision

Start insulin immediately if any of the following are present at initial assessment OR if targets are not met within 1-2 weeks of lifestyle modification: 1, 2

• Fasting glucose ≥95 mg/dL
• 1-hour postprandial ≥140 mg/dL
• 2-hour postprandial ≥120 mg/dL

Why Insulin is First-Line

• Insulin does not cross the placenta to a measurable extent, making it the safest pharmacologic option 1, 2, 4
• Insulin has unlimited dose-titration capacity without a ceiling effect 2
• Both multiple daily injections and continuous subcutaneous insulin infusion are reasonable delivery strategies, with neither shown to be superior 1

Initial Insulin Dosing

• Start with 0.7-1.0 units/kg of current maternal weight per day 2
• Allocate approximately 40% as basal insulin and 60% as prandial (mealtime) insulin 2
• Expect insulin requirements to increase by approximately 5% per week from diagnosis through week 36, often doubling by late pregnancy due to exponentially increasing insulin resistance after 16 weeks 1, 3, 2
• Frequent titration (often weekly or more) is necessary to match these changing requirements 1, 2

Insulin Types

• Rapid-acting insulin analogs (e.g., insulin aspart) are safe in pregnancy and mimic physiologic meal-related insulin release 4, 5
• Basal insulin maintains appropriate levels to cover hepatic gluconeogenesis 5

Oral Agents: When and Why to Avoid

Metformin

• NOT recommended as first-line therapy because it crosses the placenta, producing umbilical-cord concentrations equal to or higher than maternal levels 2
• The MiG-TOFU follow-up study showed children exposed to metformin in utero had higher BMI, waist-to-height ratio, and waist circumference at age 9 compared to insulin-exposed children 2
• Approximately 25-28% of women fail to achieve glycemic targets on metformin alone 2
• Absolutely contraindicated if hypertension, preeclampsia, or risk for intrauterine growth restriction develops, due to risk of fetal growth restriction or metabolic acidosis 1, 2

Glyburide

• NOT recommended as first-line therapy because it crosses the placenta, achieving fetal cord concentrations of 50-70% of maternal levels 2
• Meta-analyses show glyburide is associated with higher rates of neonatal hypoglycemia, macrosomia, and increased fetal abdominal circumference compared to insulin or metformin 1, 2
• Failed to meet non-inferiority criteria versus insulin for composite neonatal outcomes 2
• Approximately 23% of women on glyburide do not reach glycemic targets 2
• Glyburide has the poorest safety profile among available agents 2

When Oral Agents May Be Considered

Oral agents can be used only when insulin administration is impractical or unsafe due to cost, language barriers, limited health literacy, or cultural factors 1, 2

• If an oral agent must be used, metformin is preferred over glyburide due to lower incidences of neonatal hypoglycemia and macrosomia 2
• Patients must be counseled that all oral agents cross the placenta and lack long-term offspring safety data 1, 2
• If glycemic targets are not met within 1-2 weeks of oral therapy, transition promptly to insulin 2

Fetal Surveillance

Ultrasound Monitoring

• Begin serial ultrasound measurement of fetal abdominal circumference in the second or early third trimester, repeating every 2-4 weeks 2
• When fetal abdominal circumference is <75th percentile (normal growth), less intensive management may be adopted while continuing blood glucose monitoring 2
• When fetal abdominal circumference is ≥75th percentile (excessive growth), lower glycemic targets or intensify pharmacologic therapy 2

Maternal Fetal Movement Monitoring

• Instruct the patient to count fetal movements during the last 8-10 weeks of gestation and report any perceived reduction immediately 2

Maternal Surveillance

Blood Pressure and Preeclampsia Screening

• Measure blood pressure and urinary protein at every prenatal visit to detect preeclampsia, which is more common in diabetes 2
• Blood pressure targets of 110-135/85 mmHg are suggested to reduce risk of accelerated maternal hypertension while minimizing impaired fetal growth 1

Ketone Monitoring

• Provide urine ketone strips to detect inadequate caloric or carbohydrate intake, especially if on calorie-restricted diets 2
• Fasting urine ketone testing helps prevent ketosis 2
• Women with type 1 diabetes (if that is the diagnosis) need education on diabetic ketoacidosis prevention and detection, as pregnancy is a ketogenic state with DKA occurring at lower glucose levels than in non-pregnant individuals 1

Ophthalmologic Evaluation

• If preexisting type 1 or type 2 diabetes is confirmed (not GDM), obtain a baseline ophthalmology exam in the first trimester and monitor every trimester as indicated by degree of retinopathy 1
• Rapid implementation of tight glycemic control in the setting of retinopathy can worsen retinopathy 1

Medication Safety

Discontinue Potentially Harmful Medications

• Stop ACE inhibitors, angiotensin receptor blockers, and statins immediately if the patient is taking them, as they are potentially teratogenic 1
• These medications should be avoided in all sexually active women of childbearing age not using reliable contraception 1

Intrapartum Management

Labor Glucose Monitoring

• Monitor maternal capillary glucose every 1-2 hours during labor with a target range of 80-110 mg/dL to reduce risk of fetal hypoxia and neonatal hypoglycemia 2, 6
• If glucose exceeds 180 mg/dL during labor, administer an insulin bolus 2
• If glucose exceeds 297 mg/dL, delay non-urgent procedures and give corrective insulin 2

Insulin Requirements After Delivery

• Insulin resistance drops rapidly with delivery of the placenta 1
• Women become very insulin sensitive immediately following delivery and may initially require much less insulin than in the prepartum period 1
• Particular attention should be directed to hypoglycemia prevention in the setting of breastfeeding and erratic sleep and eating schedules 1

Delivery Timing

• For women requiring insulin or with suboptimal glycemic control, delivery is recommended at 39 weeks (39⁰–39⁶ weeks) 2
• For women with diet-controlled GDM meeting glycemic targets, delivery at 39-40 weeks is appropriate 2
• Pregnancies complicated by diabetes should generally not go beyond term 7

Postpartum Follow-Up

Immediate Postpartum Testing

• Perform a 75-g oral glucose tolerance test at 4-12 weeks postpartum using non-pregnancy diagnostic criteria to identify persistent diabetes or prediabetes 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

Long-Term Diabetes Risk

• Women with a history of GDM have a 50-70% risk of developing type 2 diabetes over 15-25 years 2
• Perform lifelong screening for diabetes at least every 3 years using standard non-pregnant criteria (annual A1C, annual fasting plasma glucose, or triennial 75-g OGTT) 2
• Lifestyle intervention and metformin reduce progression to diabetes by 35% and 40%, respectively, over 10 years 1, 7, 8

Breastfeeding

• Strongly encourage breastfeeding for immediate nutritional and immunologic benefits and potential longer-term metabolic advantages for both mother and child 2, 8

Common Pitfalls to Avoid

• Do not delay insulin initiation if glycemic targets are not met within 1-2 weeks of lifestyle modification; early insulin use improves outcomes 1, 2
• Do not start oral agents before attempting insulin as first-line therapy; the safety concerns of placental transfer outweigh convenience 2
• Do not continue metformin if hypertension or preeclampsia develops; switch immediately to insulin to prevent fetal growth restriction or acidosis 1, 2
• Do not reduce carbohydrates below 175 g/day, as inadequate carbohydrate intake may compromise fetal growth when total energy intake is insufficient 2
• Do not rely on A1C alone for ongoing GDM management; daily blood glucose monitoring is essential because macrosomia results primarily from postprandial hyperglycemia, which A1C may not adequately detect 2
• Do not forget aspirin prophylaxis starting at 12-16 weeks to reduce preeclampsia risk 1