What is the recommended monitoring protocol for gestational diabetes mellitus?

Monitoring Protocol for Gestational Diabetes Mellitus

Blood Glucose Self-Monitoring

Women with GDM should perform daily self-monitoring of blood glucose (SMBG) with fasting glucose checked upon waking and postprandial glucose measured after each main meal (breakfast, lunch, dinner). 1

Specific Testing Schedule

• Fasting glucose: Check daily upon waking 1
• Postprandial glucose: Check after breakfast, lunch, and dinner 1
• Choose either 1-hour OR 2-hour postprandial measurements consistently throughout pregnancy—do not alternate between the two 1
• Postprandial monitoring is superior to preprandial monitoring alone and reduces risk of preeclampsia 1

Glycemic Targets

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

When to Escalate Therapy

• If targets are not achieved within 1-2 weeks of medical nutrition therapy alone, initiate insulin as first-line pharmacologic agent 1
• Daily SMBG is superior to intermittent office monitoring of plasma glucose 2

Fetal Surveillance

Ultrasound measurement of fetal abdominal circumference should begin in the second and early third trimesters and be repeated every 2-4 weeks to guide management intensity. 2, 1

Fetal Growth Monitoring Algorithm

• Normal growth (fetal abdominal circumference <75th percentile): Less intensified management may be allowed, though some SMBG should continue 2
• Excessive growth (fetal abdominal circumference ≥75th percentile): Lower glycemic targets should be selected OR pharmacologic therapy should be added/intensified 2
• This approach provides useful information when combined with maternal SMBG levels to guide management decisions 2

Fetal Movement Monitoring

• Teach mothers to monitor fetal movements during the last 8-10 weeks of pregnancy 2, 3
• Instruct patients to report immediately any reduction in perception of fetal movements 2

Additional Fetal Surveillance

• Women with fasting glucose >105 mg/dL or pregnancy progressing past term require increased surveillance for fetal demise 2
• No fetal surveillance method always detects fetal compromise 2
• Data are insufficient to determine whether surveillance beyond self-monitoring of fetal movements is indicated in women meeting glycemic targets with diet alone and appropriate fetal growth 2

Maternal Surveillance

Blood Pressure and Protein Monitoring

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. 2, 1

Ketone Monitoring

• Urine glucose monitoring is not useful in GDM 2
• Urine ketone monitoring may be useful in detecting insufficient caloric or carbohydrate intake in women treated with calorie restriction 2
• Fingerstick blood ketone testing is more representative of laboratory measurements of β-hydroxybutyrate than urine ketones 2
• However, the effectiveness of ketone monitoring (urine or blood) in improving fetal outcome has not been tested 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 target <6% (42 mmol/mol) if achievable without significant hypoglycemia 1
• Insufficient data exist to determine whether measurement of glycosylated hemoglobin is of value in routine GDM management 2

Intrapartum Monitoring

Blood glucose monitoring during labor is recommended to guide correction of maternal hyperglycemia and prevent fetal hypoxia and neonatal hypoglycemia, targeting maternal glucose 80-110 mg/dL during labor. 2, 4

• This practice is based on studies of women with pre-existing diabetes 2
• The ideal target glucose concentration during labor has not been definitively established 2

Postpartum Follow-Up

Immediate Postpartum Testing

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, 4

• 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 and require lifelong screening for diabetes at least every 3 years. 1

• Use standard non-pregnant criteria: annual HbA1c, annual fasting plasma glucose, or triennial 75-g OGTT 1

Common Pitfalls to Avoid

• Do not rely solely on fasting glucose measurements—postprandial monitoring is critical for detecting hyperglycemia that drives macrosomia 1
• Do not use urine glucose monitoring—it is not useful in GDM 2
• Do not substitute HbA1c for SMBG—HbA1c misses postprandial excursions that cause fetal complications 1
• Do not delay insulin initiation beyond 1-2 weeks if glycemic targets are not met with lifestyle modification 1
• Do not skip fetal abdominal circumference measurements—this is the key parameter for adjusting management intensity 2
• Do not forget postpartum OGTT—this is mandatory to identify persistent diabetes or prediabetes 1, 4