1. Overview & Classification
Pregnancy is a state of increased insulin resistance. Hyperglycemia during pregnancy increases risks for both mother (preeclampsia, C-section) and baby (macrosomia, shoulder dystocia, neonatal hypoglycemia).
Classification:
Pre-existing Diabetes: Type 1 or Type 2 diabetes diagnosed before pregnancy.
Gestational Diabetes Mellitus (GDM): Glucose intolerance first recognized during pregnancy.
2. Pre-Conception Care (Pre-Existing Diabetes)
For women with Type 1 or Type 2 diabetes, care begins before conception to minimize congenital malformations (which occur in the first few weeks).
A1C Target: Aim for 7.0% (ideally 6.5%) prior to conception.
Supplements: Start Folic Acid (1 mg/day) 3 months pre-conception to prevent neural tube defects.
Medication Review: Stop potentially teratogenic drugs:
ACE Inhibitors / ARBs.
Statins.
Screening: Assess for complications (retinopathy, nephropathy) as pregnancy can worsen them.
3. Diagnosis of GDM (The "Preferred" vs. "Alternative" Approach)
This is a high-yield exam topic. Canada suggests a “Preferred” 2-step approach but allows an “Alternative” 1-step approach. Screening typically occurs at 24–28 weeks gestation.
A. Preferred Approach (Sequential 2-Step)
Step 1 (Screen): 50g Oral Glucose Challenge Test (non-fasting).
< 7.8 mmol/L: Normal.
7.8 – 11.0 mmol/L: Indeterminate Go to Step 2.
11.1 mmol/L: GDM Diagnosed (No further testing needed).
Step 2 (Diagnostic): 75g Oral Glucose Tolerance Test (fasting).
Diagnosis of GDM is made if ONE value is met or exceeded:
Fasting 5.3 mmol/L
1 hour 10.6 mmol/L
2 hour 9.0 mmol/L
B. Alternative Approach (1-Step)
Test: 75g Oral Glucose Tolerance Test (fasting).
Diagnosis of GDM is made if ONE value is met or exceeded:
Fasting 5.1 mmol/L
1 hour 10.0 mmol/L
2 hour 8.5 mmol/L
4. Management Targets During Pregnancy
Targets are tighter during pregnancy to prevent macrosomia.
| Parameter | Target (mmol/L) |
| Fasting / Pre-prandial | < 5.3 |
| 1-hour Post-prandial | < 7.8 |
| 2-hour Post-prandial | < 6.7 |
| A1C | 6.5% (ideally 6.1% if safe) |
5. Management Strategies
A. Lifestyle (First Line)
Nutritional therapy is the primary intervention for GDM.
Weight Gain: Monitor gestational weight gain based on pre-pregnancy BMI (e.g., Normal BMI 18.5–24.9 should gain 11.5–16 kg).
Ketones: Avoid ketosis (starvation ketones) as it may harm the fetus.
B. Pharmacotherapy
Insulin: The Gold Standard and first-line pharmacotherapy if lifestyle fails to reach targets within 2 weeks.
Safe Insulins: Aspart, Lispro, Glargine, Detemir, NPH, Regular. (Glulisine and Degludec were not standard at time of 2018 guidelines for pregnancy).
Dosing: Needs increase dramatically in the 2nd and 3rd trimesters due to placental hormones causing insulin resistance.
Metformin: Can be used as an alternative or adjunct. It crosses the placenta.
Glyburide: Generally not recommended as first-line due to higher rates of neonatal hypoglycemia and macrosomia compared to insulin or metformin.
6. Intrapartum & Postpartum Care
Labor: Maintain maternal glucose between 4.0 – 7.0 mmol/L to prevent neonatal hypoglycemia.
Breastfeeding: Strongly encouraged. It reduces the risk of the child developing obesity/diabetes and helps maternal weight loss.
Metformin & Glyburide: Considered safe during breastfeeding.
Postpartum Screening (GDM):
Women with GDM are at high risk for Type 2 diabetes.
Test: 75g OGTT between 6 weeks and 6 months postpartum.
7. Diabetes Canada 2018 Clinical Practice Guidelines Recommendations
Key takeaways from the “Recommendations” section (Page S277).
Pre-conception: Women with diabetes should receive pre-conception care (A1C 7.0%, Folic Acid 1 mg) [Grade D, Consensus].
Screening GDM: Screen all pregnant women at 24–28 weeks [Grade C, Level 3].
Diagnosis: Use the Preferred 2-step approach (50g screen 75g diagnostic) OR the Alternative 1-step approach (75g diagnostic) [Grade B, Level 2].
Glycemic Targets: Fasting < 5.3 mmol/L, 1h < 7.8 mmol/L, 2h < 6.7 mmol/L [Grade D, Consensus].
Treatment:
Insulin is first-line [Grade A, Level 1].
Metformin may be used as an alternative [Grade A, Level 1A].
Postpartum: Screen women with GDM for diabetes between 6 weeks and 6 months postpartum using a 75g OGTT [Grade D, Consensus].
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