Description

• Gestational diabetes mellitus (GDM) is the new onset of diabetes in the second half of pregnancy.
  • Maternity care providers should distinguish between GDM and previously unrecognized type 2 diabetes mellitus (T2DM).
  • GDM that persists beyond pregnancy should be reclassified as T2DM.
• Class A1 refers to GDM controlled by diet and exercise (A1GDM).
• Class A2 refers to pharmacologically managed GDM and implies suboptimal glycemic control (A2GDM).
• GDM is associated with increased risks for preeclampsia, fetal macrosomia, shoulder dystocia, operative delivery, and subsequent T2DM and cardiovascular disease.

Epidemiology

Prevalence

• 6–8% of pregnancies in United States; may be as high as 25% with alternative diagnostic criteria (see “Diagnostic Tests & Interpretation”)
• Highest among Hispanic, African American, Native American, Asian, and Pacific Islander women
• Varies according to local prevalence of T2DM
• Increasing globally

Etiology and Pathophysiology

• The etiology of GDM is poorly understood.
• During pregnancy, the placenta produces several hormones that can cause or exacerbate insulin resistance in susceptible individuals.

Genetics

• Incompletely understood
• Strong family association
• Polygenic risk plus environmental factors

Risk Factors

• History of GDM in previous gestation
• Previous delivery of baby weighing >4 kg
• History of impaired glucose metabolism (A1c ≥5.7%, impaired glucose tolerance, or impaired fasting glucose)
• Overweight or obese (BMI ≥25 kg/m² or ≥23 kg/m² in Asian Americans) who have any of the following risk factors:
  • Physical inactivity
  • Diabetes in first-degree relative
  • High-risk ethnicity (see “Prevalence”)
  • Cardiovascular disease
  • Hypertension
  • HDL cholesterol <35 mg/dL
  • Triglyceride level >250 mg/dL
  • Polycystic ovary syndrome
  • Other clinical conditions associated with insulin resistance (e.g., prepregnancy BMI >40 kg/m², acanthosis nigricans)

General Prevention

• Weight loss or maintain healthy weight before pregnancy
• Regular exercise including both aerobic and resistance training (based on data from observational studies)

Commonly Associated Conditions

• Prediabetes
  • Impaired fasting glucose
  • Impaired glucose tolerance
  • Hemoglobin A1c 5.7–6.4%
• Hypertensive disorders of pregnancy
  • Gestational hypertension
  • Preeclampsia