Gestational diabetes (often called pregnancy diabetes) is high blood sugar that develops during pregnancy in someone who didn’t have diabetes before. It affects roughly 7-14% of pregnancies in the United States and is screened universally between 24 and 28 weeks. With diet, exercise, glucose monitoring, and insulin or metformin when needed, most women have healthy pregnancies and healthy babies. For more on screening before and during pregnancy, see our prediabetes and pregnancy guide.
Why Pregnancy Triggers Diabetes
From the second trimester onward, the placenta produces hormones – human placental lactogen, cortisol, growth hormone, and progesterone – that intentionally make the mother more insulin resistant. The biological purpose: divert glucose from the mother to the growing baby. To compensate, the mother’s pancreas typically increases insulin production by 200-250%.
If the pancreas can’t keep up, blood sugar rises – and that’s gestational diabetes mellitus (GDM). Women who already had insulin resistance, were overweight, or carried a genetic predisposition are most likely to outpace their pancreatic reserve.
Who Is at Higher Risk
Risk factors include:
- Pre-pregnancy BMI of 25 or higher
- Age 25 or older (risk rises significantly after 35)
- Family history of diabetes (parent or sibling)
- Prior gestational diabetes
- Prior baby over 9 pounds (4.1 kg) at birth
- Polycystic ovary syndrome (PCOS)
- Race/ethnicity: Hispanic/Latina, African American, Native American, Asian American, Pacific Islander
- Hypertension or cardiovascular disease history
About half of women with GDM have no obvious risk factors – which is why screening is universal.
Screening: The 1-Hour and 3-Hour Tests
The American College of Obstetricians and Gynecologists (ACOG) recommends screening between 24 and 28 weeks of pregnancy using a two-step approach:
Step 1: 1-Hour Glucose Challenge Test (GCT)
- You drink 50 g of glucose solution (no fasting required).
- Blood is drawn 1 hour later.
- If glucose is under 140 mg/dL: normal. No further testing.
- If 140 mg/dL or higher: proceed to confirmatory test.
Step 2: 3-Hour Oral Glucose Tolerance Test (OGTT)
- Fast for 8-14 hours overnight.
- Fasting blood draw, then drink 100 g glucose solution.
- Blood drawn at 1, 2, and 3 hours.
| Time Point | Carpenter-Coustan Cutoff | National Diabetes Data Group Cutoff |
|---|---|---|
| Fasting | ≥95 mg/dL | ≥105 mg/dL |
| 1 hour | ≥180 mg/dL | ≥190 mg/dL |
| 2 hours | ≥155 mg/dL | ≥165 mg/dL |
| 3 hours | ≥140 mg/dL | ≥145 mg/dL |
GDM is diagnosed when two or more values exceed the cutoffs.
One-Step Alternative
Some providers use a single 75-g 2-hour OGTT (the IADPSG criteria), with diagnosis if any one of: fasting ≥92, 1-hour ≥180, or 2-hour ≥153 mg/dL.
How Gestational Diabetes Is Managed
1. Medical Nutrition Therapy
This is the foundation of treatment. A registered dietitian helps you build a meal plan with:
- Three meals plus 2-3 snacks daily to prevent large glucose swings
- Carbohydrates limited to about 175 g/day, distributed evenly
- Smaller breakfast carbs (often 30 g) – morning insulin resistance is highest
- Pairing every carb with protein and fat to slow absorption
- Plenty of non-starchy vegetables and adequate protein for fetal growth
2. Glucose Monitoring
You’ll typically check four times daily: fasting and 1 or 2 hours after each meal. ACOG targets:
- Fasting: under 95 mg/dL
- 1 hour after meals: under 140 mg/dL
- 2 hours after meals: under 120 mg/dL
3. Physical Activity
30 minutes of moderate exercise on most days – walking, prenatal yoga, swimming, stationary cycling – significantly improves insulin sensitivity and lowers post-meal glucose.
4. Medication
If diet and exercise aren’t enough (about 15-30% of cases), insulin is the first-line medication during pregnancy because it doesn’t cross the placenta. Metformin is an oral alternative, though it does cross the placenta and long-term effects on the child are still being studied.
Effects on the Baby
Uncontrolled GDM can lead to:
- Macrosomia: Babies over 9 lbs, increasing the risk of cesarean delivery and shoulder dystocia at birth.
- Neonatal hypoglycemia: Baby’s pancreas, used to high glucose, overproduces insulin and becomes hypoglycemic after birth.
- Respiratory distress: Lung maturation may be delayed.
- Polycythemia and hyperbilirubinemia: More red blood cells and resulting jaundice.
- Long-term: Higher risk of obesity and type 2 diabetes during the child’s life.
With well-controlled glucose, most of these risks are minimized to baseline.
Effects on the Mother
- During pregnancy: Higher rates of preeclampsia, polyhydramnios (excess amniotic fluid), and cesarean delivery.
- After delivery: 50-60% lifetime risk of developing type 2 diabetes.
- Future pregnancies: 30-70% chance of recurrence.
Delivery Considerations
Most women with well-controlled GDM can deliver vaginally at term (39-40 weeks). For women on insulin, ACOG often recommends delivery by 39 weeks 6 days. Cesarean is considered if the estimated fetal weight exceeds 4,500 g (about 9 lb 14 oz). Glucose levels are monitored during labor; the baby is typically checked for hypoglycemia 30 minutes to 2 hours after birth.
Postpartum: What Happens Next
- Glucose normalizes within hours to days for most women, as placental hormones drop.
- 4-12 week postpartum screening with a 75-g 2-hour OGTT is recommended to detect persistent diabetes.
- If normal, screen with A1C or fasting glucose every 1-3 years for life.
- Breastfeeding is encouraged – it improves maternal glucose metabolism and may reduce future diabetes risk.
- Lifestyle change matters: Sustained weight loss and physical activity can cut the lifetime type 2 diabetes risk roughly in half.
Comparison: GDM vs. Pre-Existing Diabetes in Pregnancy
| Feature | Gestational Diabetes | Pre-Existing Type 1/2 Diabetes |
|---|---|---|
| Onset | Diagnosed during pregnancy | Diagnosed before pregnancy |
| Screening | 1-hour GCT at 24-28 weeks | A1C at first prenatal visit |
| First-line treatment | Diet/exercise; insulin if needed | Insulin (often pump or basal-bolus) |
| Birth defect risk | Not increased above baseline | Higher if A1C elevated at conception |
| Postpartum resolution | Usually resolves | Persists – lifelong condition |
For more on the underlying physiology, see our explainer on insulin resistance vs diabetes.
Practical Tips If You’re Diagnosed
- Ask your OB for a referral to a registered dietitian who specializes in GDM – usually covered by insurance.
- Pick a glucose meter you find easy to use; you’ll be testing 4+ times a day for the rest of pregnancy.
- Walk for 10-15 minutes after each meal – one of the most effective ways to lower post-meal glucose.
- Don’t skip carbs entirely; the baby needs glucose. Focus on slow, fiber-rich carbs.
- Track your fasting and post-meal numbers in an app or journal to share at every visit.
- Plan postpartum follow-up before you leave the hospital – it’s commonly missed.
The Bottom Line
Gestational diabetes is common, screenable, and manageable. With dietary changes, regular activity, glucose monitoring, and insulin or metformin if needed, the vast majority of women have healthy pregnancies and healthy babies. After delivery, blood sugar usually returns to normal – but the diagnosis is also a long-term flag. Postpartum screening, sustained lifestyle change, and regular follow-up testing are the most important things you can do to prevent type 2 diabetes in the years ahead.
