Normal Blood Glucose Targets in Pregnancy
For pregnant women with gestational diabetes or pre-existing diabetes, the recommended targets are: fasting glucose <95 mg/dL (5.3 mmol/L), 1-hour postprandial <140 mg/dL (7.8 mmol/L), and 2-hour postprandial <120 mg/dL (6.7 mmol/L). 1, 2
Target Glucose Values
The most recent American Diabetes Association guidelines (2023) establish clear glycemic targets for all pregnant women with diabetes, whether gestational or pre-existing 1:
Fasting Blood Sugar (FBS)
- Target: 70-95 mg/dL (3.9-5.3 mmol/L) 1
- The upper limit of 95 mg/dL is the critical threshold for treatment decisions 1, 2
- The lower limit of 70 mg/dL protects against hypoglycemia while the upper limit prevents fetal complications 1
Postprandial Blood Sugar (PPBS)
You have two monitoring options 1:
Option 1: One-hour postprandial
Option 2: Two-hour postprandial
Monitoring Strategy
For Women with Gestational Diabetes
- Perform fasting and postprandial blood glucose monitoring daily 1
- Postprandial monitoring is superior to preprandial monitoring for achieving optimal outcomes and reducing preeclampsia risk 1
- Check fasting glucose every morning and either 1-hour or 2-hour after each meal 1, 3
For Women with Pre-existing Diabetes (Type 1 or Type 2)
- More intensive monitoring is required with at least 4 measurements daily 1
- Include preprandial testing when using insulin pumps or basal-bolus therapy to adjust rapid-acting insulin doses 1
Critical Thresholds for Treatment Decisions
When to Initiate Insulin Therapy
If medical nutrition therapy fails to maintain glucose below these levels, insulin therapy must be started 1, 3:
- Fasting glucose ≥95 mg/dL 1, 2
- 1-hour postprandial ≥140 mg/dL 1, 2
- 2-hour postprandial ≥120 mg/dL 1, 2
Early Pregnancy Screening Thresholds
At the first prenatal visit, different thresholds apply for diagnosis 2:
- Fasting glucose <92 mg/dL: Normal, retest at 24-28 weeks 2
- Fasting glucose 92-125 mg/dL: Early gestational diabetes, start treatment immediately 2
- Fasting glucose ≥126 mg/dL: Overt pre-existing diabetes, not gestational diabetes 2, 4, 5
HbA1c Targets
Target HbA1c <6% (42 mmol/mol) if achievable without significant hypoglycemia 1, 2
- HbA1c may be relaxed to <7% (53 mmol/mol) if needed to prevent hypoglycemia 1
- HbA1c should be measured monthly during pregnancy due to increased red blood cell turnover 1
- Important caveat: HbA1c is a secondary measure; self-monitoring of blood glucose is the primary tool for day-to-day management 1
Common Pitfalls to Avoid
Timing of Postprandial Measurements
- Measure 1-hour postprandial after breakfast (highest abnormal rate occurs at this time) 6
- Measure 2-hour postprandial after dinner (highest abnormal rate occurs at this time) 6
- The rate of abnormal values is 2.5-fold greater at 1-hour post-breakfast versus 2-hour post-breakfast 6
Fasting Glucose Monitoring
- Never omit fasting glucose measurements 7
- While normal fasting glucose (<105 mg/dL) predicts normal 2-hour postprandial values 96% of the time, fasting glucose is the most critical value for treatment decisions 7
- Fasting glucose >105 mg/dL requires immediate insulin therapy regardless of postprandial values 1
Hypoglycemia Risk
- Women with type 1 diabetes may struggle to achieve these targets without hypoglycemia, particularly those with hypoglycemia unawareness 1
- In early pregnancy (first trimester), insulin requirements decrease and hypoglycemia risk increases 1
- If targets cannot be achieved safely, slightly higher individualized targets may be necessary 1
Physiologic Context
Normal Pregnancy Changes
- Fasting glucose decreases by approximately 3 mg/dL in the first trimester (from 81 to 78 mg/dL) 8
- Further slight decrease occurs in the third trimester (median 76 mg/dL) 8
- After delivery, fasting glucose increases sharply (84 mg/dL in puerperium) 8