Gestational Diabetes

Gestational diabetes mellitus (GDM) is glucose intolerance first recognized in pregnancy. It affects 5–10% of pregnancies. With monitoring and treatment most pregnancies progress well. Standard screening is at 24–28 weeks.

Why it happens

Placental hormones (estrogen, cortisol, human placental lactogen) raise insulin resistance in late pregnancy. If maternal pancreatic insulin output cannot compensate, blood glucose rises. Most cases resolve after delivery, but lifetime type-2 diabetes risk rises about sevenfold.

Risk factors

• BMI ≥ 25
• Age 35+
• Family history of diabetes
• Prior GDM
• Previous baby ≥ 4 kg
• PCOS
• Twin pregnancy

Screening

Two common approaches:

• Two-step (US standard): 50 g non-fasting → 1-hour blood draw. If ≥ 140 mg/dL, proceed to 100 g 3-hour OGTT.
• One-step (75 g): fasting → 75 g → 1-hour and 2-hour draws.

100 g 3-hour OGTT diagnostic cutoffs

Two or more values at/above any of these confirm GDM:

• Fasting: ≥ 95 mg/dL
• 1 hour: ≥ 180 mg/dL
• 2 hour: ≥ 155 mg/dL
• 3 hour: ≥ 140 mg/dL

Diet

• Carbohydrate distribution: 40–50% of calories, split across 3 meals + 2–3 snacks.
• Limit simple sugars: sugar, juice, desserts, honey, syrups.
• Choose low-GI: whole grains, beans, vegetables, nuts.
• Pair carbs with protein: lean meat, eggs, beans at every meal.
• Add fiber: vegetables, fruit, whole grains.
• Breakfast is the toughest: morning hormones keep glucose high — keep carbs minimal.

Self-monitoring targets

After diagnosis, test 4–7 times daily as directed.

• Fasting: ≤ 95 mg/dL
• 1 h after meals: ≤ 140 mg/dL
• 2 h after meals: ≤ 120 mg/dL

Medication

If diet and exercise miss targets, insulin (does not cross the placenta — safest) or metformin (by clinician decision) is added.

Effects on baby and mother

• Macrosomia (≥ 4 kg): harder delivery and higher C-section rate.
• Neonatal hypoglycemia: monitored in the first 24 hours.
• Jaundice: more common.
• Higher gestational hypertension/preeclampsia risk.
• Long-term: maternal type-2 diabetes risk and childhood obesity/diabetes risk both rise.

Postpartum

Most cases resolve after birth. Recheck with a 75 g OGTT at 6–12 weeks postpartum, then routine diabetes screening every 1–3 years for life.

Related calculators

• Pregnancy weight gain Track cumulative gain against the IOM recommended range by pre-pregnancy BMI
• Due date Calculate pregnancy week and due date from your last period

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• Morning Sickness The most common symptom of weeks 6–12 — timing, severity, and relief
• Pregnancy Foods What to eat, what to avoid, and what to limit
• Pregnancy Exercise Safe workouts by trimester — what to do and what to skip
• Pregnancy Weight Gain Recommended range by BMI, weekly targets, gaining too much or too little