Gestational diabetes

What gestational diabetes is

Gestational diabetes is high blood sugar that develops during pregnancy in someone who didn't have diabetes before. It happens when pregnancy hormones (especially from the placenta) make your body less responsive to insulin — a state called insulin resistance. Your pancreas usually compensates by making more insulin, but if it can't keep up, blood sugar rises.

It typically develops in the second half of pregnancy and resolves shortly after delivery. About 6–9% of US pregnancies are affected — it's the most common medical complication of pregnancy.

The condition is well-understood and well-managed. The vast majority of people with gestational diabetes have healthy pregnancies and healthy babies, especially when blood sugar is kept within target range through diet, exercise, monitoring, and (sometimes) medication.

Risk factors

Gestational diabetes is more common in people who are over 35, have a higher pre-pregnancy BMI, have a family history of type 2 diabetes, have previously had a baby weighing over 4 kg (about 9 lb), or have PCOS. People of South Asian, Black, Hispanic, Pacific Islander, and Indigenous backgrounds also have higher rates, for reasons that are partly genetic and partly related to social determinants of health.

That said, gestational diabetes can happen to anyone — including people with no risk factors at all. That's why universal screening (around 24–28 weeks) is standard practice in most countries.

How it's diagnosed

The standard screening in the US is a two-step process. First, the one-hour glucose challenge test: you drink a sugary solution (50 g glucose), then have blood drawn an hour later. If your blood sugar is above the cutoff (usually 130–140 mg/dL depending on the lab), you move to the three-hour glucose tolerance test (GTT) for confirmation.

In the three-hour GTT, you fast, have a baseline blood draw, drink a 100 g glucose solution, and have blood drawn at 1, 2, and 3 hours. If two or more readings are above target, the diagnosis is gestational diabetes.

Many providers in other countries (and some in the US) use a one-step 75 g GTT instead, with results read at 1 and 2 hours. The diagnosis criteria differ slightly between protocols, but the outcomes are similar.

Management: diet, monitoring, exercise

First-line treatment is diet plus blood-sugar monitoring. Most people are referred to a registered dietitian (often a Certified Diabetes Educator) who tailors a plan to your usual eating patterns. The principles: distribute carbohydrates across the day in smaller portions, pair carbs with protein and fat to slow absorption, and limit added sugars and refined carbs (white rice, sugary drinks, sweets).

Blood-sugar monitoring uses a home glucose meter, typically 4 times a day: fasting (before breakfast) and 1 or 2 hours after each meal. Targets vary slightly by provider but commonly: fasting under 95 mg/dL, 1-hour postmeal under 140 mg/dL (or 2-hour under 120 mg/dL).

Exercise — even modest walking after meals — helps move glucose into muscle cells and lowers post-meal numbers. 30 minutes of moderate activity most days is the typical recommendation, but anything is better than nothing.

About 70–85% of people with gestational diabetes can manage with diet and exercise alone. The rest need medication.

When medication is needed

If diet and exercise aren't keeping blood sugar in range, your provider will recommend medication. The two main options are insulin (injected) and metformin (oral). Both are safe in pregnancy; the choice depends on which numbers are out of range, your preferences, and your provider's protocols.

Insulin doesn't cross the placenta and has decades of safety data. Metformin does cross the placenta in small amounts; long-term studies of children exposed to metformin in utero have been reassuring but slightly less extensive than insulin's.

Starting medication isn't a failure — it just means your body needed extra help during pregnancy. Most people who need medication discontinue it immediately after delivery.

What it means for your baby

Well-controlled gestational diabetes is associated with normal pregnancy outcomes. Poorly controlled blood sugar increases the risk of macrosomia (larger-than-average baby, which raises C-section and birth-injury risk), preterm birth, neonatal hypoglycemia (low blood sugar in the baby right after birth), and respiratory issues at birth.

After birth, babies of mothers with gestational diabetes are typically monitored briefly for blood sugar levels. Most are fine after a feeding or two; a small number need IV glucose support for a day or two.

Longer-term, children whose mothers had gestational diabetes have a slightly higher lifetime risk of obesity and type 2 diabetes — driven by both genetic and environmental factors. The risk isn't deterministic; healthy childhood habits make a real difference.

After delivery

Gestational diabetes resolves immediately after delivery in most cases. Blood sugar is usually re-checked at the postpartum visit (6–12 weeks) with a 75 g GTT to confirm normal glucose tolerance.

Having had gestational diabetes increases your lifetime risk of type 2 diabetes substantially — about 50% within 5–10 years. Annual or biennial blood-sugar screening is recommended for life. Lifestyle factors (weight management, regular activity, balanced diet) substantially reduce that risk.

Frequently asked questions

Sources and medical references

• ACOG — Pregnancy complications — Frequently Asked Questions
• Mayo Clinic — Pregnancy week-by-week and complications overview
• NHS — Pregnancy complications
• Mayo Clinic — Gestational diabetes