Blood Glucose Monitoring Schedule in Gestational Diabetes
Women with gestational diabetes should perform daily self-monitoring of fasting and postprandial blood glucose, specifically checking fasting glucose and either 1-hour or 2-hour postprandial values after each meal. 1, 2
Recommended Monitoring Frequency
Daily monitoring should include:
- Fasting glucose measurement each morning 1, 2
- Postprandial glucose after each meal (breakfast, lunch, and dinner) 1, 2
- Either 1-hour OR 2-hour postprandial measurements, though evidence suggests postprandial monitoring is superior to preprandial monitoring 1, 3
Target Glucose Values
The American Diabetes Association establishes clear thresholds that guide treatment decisions 1, 2:
Fasting: <95 mg/dL (5.3 mmol/L) 1, 2
1-hour postprandial: <140 mg/dL (7.8 mmol/L) 1, 2
2-hour postprandial: <120 mg/dL (6.7 mmol/L) 1, 2
Clinical Evidence Supporting Postprandial Monitoring
Postprandial monitoring demonstrates superior outcomes compared to preprandial monitoring. A landmark randomized trial showed that women using postprandial glucose measurements (1-hour after meals) had significantly better glycemic control, with infants experiencing lower rates of neonatal hypoglycemia (3% vs. 21%), macrosomia (12% vs. 42%), and cesarean delivery for cephalopelvic disproportion (12% vs. 36%) compared to preprandial monitoring 3. This evidence strongly supports the current guideline recommendations prioritizing postprandial measurements 1.
Timing Considerations: 1-Hour vs. 2-Hour Postprandial
The choice between 1-hour and 2-hour postprandial monitoring can be tailored to meal timing, though both are acceptable 2. Research reveals that glucose peaks vary by meal: abnormal values occur 2.5-fold more frequently at 1-hour post-breakfast compared to 2-hours, while the opposite pattern emerges post-dinner with 2-fold higher abnormal values at 2-hours 4. Despite these variations, both 1-hour and 2-hour monitoring strategies achieve adequate glycemic control when appropriate targets are used 1, 2.
Practical Implementation
Self-monitoring of blood glucose (SMBG) using capillary blood glucose meters is the standard approach, which is superior to intermittent office-based plasma glucose monitoring 1. Glucose meters must report plasma-equivalent values and meet FDA accuracy standards 1.
Measurements should be taken:
- Fasting: immediately upon waking, before any food or drink 1
- Postprandial: starting the timer from the beginning of the meal 2
- Using proper technique with calibrated meters intended for professional or home use 1
When to Intensify Monitoring or Treatment
Insulin therapy should be initiated when medical nutrition therapy fails to maintain glucose within target ranges 1. Specifically, insulin is recommended when fasting glucose ≥95 mg/dL, 1-hour postprandial ≥140 mg/dL, or 2-hour postprandial ≥120 mg/dL persist despite dietary management 1, 2, 5.
For women requiring insulin therapy, more frequent monitoring may be necessary, including preprandial measurements to guide rapid-acting insulin dosing adjustments 1. The frequency should be appropriate for the insulin regimen, typically at least 4 times daily for those on multiple daily injections 1.
Role of Continuous Glucose Monitoring (CGM)
While traditional SMBG remains the standard, continuous glucose monitoring can detect glycemic fluctuations missed by standard testing 6. However, CGM is not routinely recommended for all women with GDM at this time, though research is ongoing 1. CGM has demonstrated value in pregnant women with type 1 diabetes but requires further study in GDM populations 1.
Common Pitfalls to Avoid
Do not rely on urine glucose monitoring, as it is not useful in GDM management 1.
Do not use HbA1c as the primary monitoring tool in GDM, as physiological increases in red blood cell turnover during pregnancy cause A1C to fall, and it may not capture postprandial hyperglycemia that drives macrosomia 1, 2. HbA1c should only serve as a secondary measure 1.
Avoid skipping postprandial measurements in favor of only fasting and preprandial values, as postprandial hyperglycemia is the primary driver of fetal macrosomia and adverse outcomes 2, 3.
Do not delay insulin initiation when glucose targets are consistently exceeded, as this increases risks of macrosomia, neonatal hypoglycemia, and preeclampsia 5.
Additional Monitoring Considerations
Urine ketone monitoring may be useful in women treated with calorie restriction to detect insufficient caloric or carbohydrate intake 1. However, avoid excessive carbohydrate restriction that could lead to ketosis 2.
Maternal surveillance should include blood pressure and urine protein monitoring to detect hypertensive disorders, with increased fetal surveillance when fasting glucose exceeds 95 mg/dL or pregnancy progresses past term 1.