Fasting Glucose (Plasma)
Fasting plasma glucose decreases slightly during normal pregnancy due to increased placental glucose uptake and insulin sensitivity changes. Elevated fasting glucose is the primary screening marker for gestational diabetes mellitus.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| mg/dL | 75 – 99 | — | 75 – 80 | 71 – 77 |
| mmol/L | 4.2 – 5.5 | — | 4.2 – 4.4 | 4.0 – 4.3 |
Causes of low fasting glucose in pregnancy
- Normal pregnancy physiology with increased fetal glucose utilization
- Prolonged fasting or inadequate caloric intake
- Hyperemesis gravidarum
- Insulin overdose or sulfonylurea exposure
- Reactive hypoglycemia
- Acute or chronic liver disease
- Sepsis or critical illness
- Adrenal insufficiency
- Insulinoma (rare)
Causes of high fasting glucose in pregnancy
- Gestational diabetes mellitus (GDM)
- Overt (preexisting) diabetes mellitus — type 1 or type 2
- Obesity and insulin resistance
- Polycystic ovary syndrome (PCOS)
- Glucocorticoid therapy (betamethasone, prednisone)
- Cushing syndrome or cortisol excess
- Stress hyperglycemia
- Medications (β-blockers, atypical antipsychotics, niacin)
Diagnostic thresholds in pregnancy
- Gestational diabetes mellitus (GDM): Fasting glucose ≥ 92 mg/dL (5.1 mmol/L) and < 126 mg/dL.
- Overt diabetes in pregnancy: Fasting glucose ≥ 126 mg/dL (7.0 mmol/L).
- Thresholds based on IADPSG, ADA, and WHO diagnostic criteria.
References
- Kratz A, Ferraro M, Sluss PM, Lewandrowski KB. Laboratory reference values. N Engl J Med. 2004.
- International Association of Diabetes and Pregnancy Study Groups (IADPSG). Diabetes Care. 2010.
- Expert Committee on Diagnosis and Classification of Diabetes Mellitus. Diabetes Care. 2003.
- Cousins L et al. Glucose physiology in pregnancy. Am J Obstet Gynecol. 1980.