Gdm
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GDM = Gestational Diabetes Mellitus. Let me search the library now.
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"gestational diabetes mellitus" diagnosis management
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Here is a thorough overview of Gestational Diabetes Mellitus (GDM):
Gestational Diabetes Mellitus (GDM)
Definition
GDM is glucose intolerance first diagnosed during pregnancy that is not clearly pre-existing diabetes. Pathophysiology mirrors type 2 DM: advancing pregnancy causes significant insulin resistance (driven largely by placentally produced hormones, especially human placental lactogen), and a subset of women cannot maintain adequate compensatory insulin secretion. A small proportion (~6%) actually have pre-type 1 diabetes that manifests during pregnancy.
- Prevalence: ~5-9% of pregnancies (two-step method) or ~8% overall
Risk Factors
- Obesity
- Age >25 years
- Family history of T2DM or prior GDM
- Ethnic groups: Hispanic, Native American, Asian, African American
- Glucosuria on routine testing
Screening & Diagnosis
When to Screen
- 24-28 weeks gestation (routine for all women)
- Earlier in high-risk women (glucosuria, obesity, prior GDM, strong family history)
- USPSTF: B recommendation for screening after 24 weeks; insufficient evidence before 24 weeks
Two-Step Approach (US standard - ADA/ACOG)
Step 1 - 50-g Glucose Challenge Test (GCT):
- Given in fasting or non-fasting state
- Plasma glucose at 1 hour
- Positive threshold: ≥130-140 mg/dL (provider discretion; 130 mg/dL more sensitive, 140 mg/dL more specific)
Step 2 - 100-g, 3-hour OGTT (if Step 1 positive):
| Time Point | Threshold (Carpenter/Coustan) |
|---|---|
| Fasting | ≥95 mg/dL |
| 1 hour | ≥180 mg/dL |
| 2 hours | ≥155 mg/dL |
| 3 hours | ≥140 mg/dL |
- 2 or more abnormal values = GDM diagnosis
- ACOG 2018 notes women with even 1 abnormal value may be treated
One-Step Approach (IADPSG/WHO - international)
- 75-g, 2-hour OGTT at 24-28 weeks
- GDM diagnosed if any single value meets or exceeds:
| Time Point | Threshold |
|---|---|
| Fasting | ≥92 mg/dL (5.1 mmol/L) |
| 1 hour | ≥180 mg/dL (10.0 mmol/L) |
| 2 hours | ≥153 mg/dL (8.5 mmol/L) |
- Overt diabetes if fasting ≥126 mg/dL, 2-h ≥200 mg/dL, HbA1c ≥6.5%, or random glucose ≥200 mg/dL
Maternal & Fetal Complications
- Macrosomia / large for gestational age (LGA)
- Shoulder dystocia
- Preeclampsia
- Polyhydramnios
- Fetal distress / fetal demise
- Neonatal hypoglycemia (from fetal hyperinsulinemia)
- Increased cesarean delivery rate
- Long-term: GDM confers a 7-10-fold increased risk of T2DM; ~10% risk within 5 years of delivery
Management
Glycemic Targets in Pregnancy
| Timing | Target |
|---|---|
| Fasting | <95 mg/dL (<5.3 mmol/L) |
| 1-hour postprandial | <140 mg/dL (<7.8 mmol/L) |
| 2-hour postprandial | <120 mg/dL (<6.7 mmol/L) |
First-line: Medical Nutrition Therapy (MNT)
- Effective in the majority of GDM women
- Aim to optimize normoglycemia and appropriate gestational weight gain
Pharmacotherapy (when MNT insufficient):
- Insulin - preferred therapy (safest profile, lowest treatment failure rate)
- Insulin needs increase across trimesters: 0.7-0.8 u/kg (T1) → 0.8-1.0 u/kg (T2) → 0.9-1.2 u/kg (T3)
- Typically basal + prandial regimen
- Metformin - alternative if patient declines/cannot take insulin; lower mean birth weights, gestational weight gain, and preeclampsia vs. insulin; however, unknown long-term effects on child metabolic programming (higher childhood adiposity) inform preference for insulin
- Glyburide - another oral alternative; now less preferred due to higher neonatal hypoglycemia risk vs. metformin
Monitoring
- Fasting and 1- or 2-hour postprandial glucose daily minimum
- HbA1c has limited utility in pregnancy (falsely low due to increased RBC turnover)
- Continuous glucose monitoring (CGM) is evidence-based for T1DM in pregnancy; role in GDM evolving
- Serial ultrasounds for LGA / polyhydramnios
Delivery
- Induction considered at 37-39 weeks
- Cesarean reserved for estimated fetal weight ≥4500 g (to minimize shoulder dystocia risk)
- Tight glycemic control at delivery to prevent neonatal hypoglycemia
Postpartum Follow-up
- 2-hour 75-g OGTT at 4-12 weeks postpartum to screen for persistent diabetes or impaired glucose tolerance
- All women should be counseled on long-term T2DM and cardiovascular risk
- Exercise, weight loss, and metformin reduce subsequent T2DM risk in these women
Sources: Creasy & Resnik's Maternal-Fetal Medicine, p. 1427 | Harrison's Principles of Internal Medicine 22E | Textbook of Family Medicine 9e
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