What is gestational diabetes?

Gestational Diabetes Mellitus (GDM)

Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance with onset or first recognition during pregnancy, regardless of whether insulin or only diet modification is used for treatment and whether the condition persists after pregnancy. 1, 2

Definition and Prevalence

• GDM affects approximately 7% of all pregnancies, resulting in more than 200,000 cases annually in the United States 1
• The prevalence varies widely from 1% to 14% depending on the population studied and diagnostic criteria used 1, 2
• Higher prevalence rates are observed in certain ethnic groups and regions, with the Middle East and North Africa having rates as high as 12.9%, while Europe has lower rates around 5.8% 2
• GDM represents nearly 90% of all pregnancies complicated by diabetes 1

Risk Factors

Several factors increase the risk of developing GDM:

• Marked obesity
• Personal history of GDM in previous pregnancies
• Glycosuria
• Strong family history of diabetes
• Age older than 25 years
• Belonging to certain ethnic groups with high diabetes prevalence
• Polycystic ovary syndrome 1, 2

Women considered low-risk (who may not require glucose testing) are those who meet all of the following criteria:

• Age younger than 25 years
• Normal weight before pregnancy
• No family history of diabetes
• No history of abnormal glucose metabolism
• No history of poor obstetric outcomes 1

Pathophysiology

• Normal pregnancy is characterized by progressive insulin resistance that begins mid-pregnancy and progresses through the third trimester
• GDM occurs when pancreatic β-cells cannot increase insulin production sufficiently to overcome the insulin resistance of pregnancy
• This results in maternal hyperglycemia that can affect fetal development 1, 2

Diagnosis

The diagnosis of GDM typically follows one of two approaches:

One-step approach

• Perform a diagnostic oral glucose tolerance test (OGTT) without prior screening
• Recommended for high-risk populations 1

Two-step approach

• Initial screening with a 50g glucose challenge test (GCT)
• If threshold is exceeded, proceed to a diagnostic OGTT
• More commonly used in average-risk populations 1

Diagnostic criteria with 100g oral glucose load (two or more values must be met or exceeded):

Time	Plasma Glucose (mg/dl)	mmol/l
Fasting	95	5.3
1-hour	180	10.0
2-hour	155	8.6
3-hour	140	7.8
[1,2]

Complications

GDM is associated with significant short-term and long-term health risks:

Maternal complications:

• Increased risk of preeclampsia and eclampsia
• Higher rates of cesarean delivery
• Increased risk of developing type 2 diabetes after pregnancy (20-50% within 5-10 years) 2, 3

Fetal/neonatal complications:

• Macrosomia (large for gestational age)
• Neonatal hypoglycemia (10-40% prevalence)
• Respiratory distress syndrome
• Birth trauma (shoulder dystocia, brachial plexus injury)
• Higher risk of obesity and glucose intolerance in late adolescence and young adulthood 1, 2

Management

The cornerstone of GDM management is glycemic control:

1. Medical Nutrition Therapy (MNT):

   • First-line treatment
   • Individualized dietary plan with appropriate caloric intake and carbohydrate distribution

2. Self-monitoring of blood glucose (SMBG):

   • Superior to intermittent office monitoring
   • Postprandial monitoring appears more effective than preprandial for insulin-treated women 1

3. Physical activity:

   • Regular moderate exercise helps improve insulin sensitivity

4. Medication:

   • Indicated when MNT fails to maintain target glucose levels
   • Insulin is the traditional first-line medication
   • Oral agents (metformin, glyburide) may be considered in selected cases 2, 4

Target glucose levels for treatment:

• Fasting plasma glucose < 95 mg/dl (5.3 mmol/l)
• 1-h postprandial plasma glucose < 140 mg/dl (7.8 mmol/l)
• 2-h postprandial plasma glucose < 120 mg/dl (6.7 mmol/l) 1

Postpartum Follow-up

• Women with GDM should undergo glucose testing 6-12 weeks postpartum to identify persistent diabetes
• Annual glucose and HbA1c testing is recommended for early detection of type 2 diabetes
• Lifestyle modifications (weight management, healthy diet, regular physical activity) are crucial for preventing or delaying progression to type 2 diabetes 2, 5

Prevention Strategies

• Preconception weight management
• Regular physical activity before and during pregnancy
• Healthy dietary patterns
• Breastfeeding may reduce obesity risk in children 2, 6

GDM represents a significant opportunity to identify women at high risk for future diabetes and implement preventive strategies that can benefit both mother and child long-term.