Is one high value enough for a gestational diabetes diagnosis?

Yes: with the 75 g load, a single value at or above the threshold (92 fasting, 180 at 1 hour, 153 at 2 hours mg/dL) is enough.

The glucose curve in pregnancy (OGTT): how it works and the values

What the glucose curve in pregnancy is

The glucose curve — also called the oral glucose tolerance test (OGTT) — is the exam used to diagnose gestational diabetes. It measures how the body handles sugar after drinking a known amount of glucose: if blood sugar rises too much, it means the body is struggling to control it during pregnancy.

When it is done

In most cases it is performed between weeks 24 and 28. With risk factors (excess weight, family history of diabetes, previous gestational diabetes, older age) the doctor may bring it forward, often between weeks 16 and 18, and then repeat it at 24-28 weeks if the first was normal.

How it works

You arrive fasting (usually 8-12 hours) and a first blood sample is taken (baseline glucose).
You drink a solution with 75 g of glucose.
Two more samples are taken, at 60 and 120 minutes.
While waiting you stay seated and at rest, without eating, smoking or walking around much.

The reference values

With the 75 g load, gestational diabetes is diagnosed if even a single one of these values is equal to or above:

Fasting: 92 mg/dL (5.1 mmol/L)
After 1 hour: 180 mg/dL (10.0 mmol/L)
After 2 hours: 153 mg/dL (8.5 mmol/L)

If all three values stay below these thresholds, the test is negative. But a single value at or above the threshold is enough to make the diagnosis.

How to prepare

In the days before, keep a normal diet without cutting carbohydrates: a diet too low in carbs can distort the result. On the day, come fasting, bring something to read (it lasts about 2 hours) and avoid exertion. Always follow the lab's instructions.

What if the result is positive?

A diagnosis of gestational diabetes is not a reason to panic: in most cases it is managed with diet, physical activity and blood-sugar monitoring, and only some cases need medication. The goal is to keep blood sugar in range until delivery, reducing the risks for mother and baby, always followed by the doctor and obstetrician. (More: gestational diabetes.)

The role of urine glucose screening

Glucose in the urine is common in pregnancy and can prompt attention, but it does not replace the OGTT: the diagnosis is made from blood. A urine screen can be an extra signal between check-ups, to mention to your doctor. (See: glucose in urine during pregnancy.)

Frequently asked questions

Does the glucose curve harm the baby? No. It is a safe, routine test in pregnancy; the glucose you drink does not harm the baby.

Can I eat before the test? No, it must be done fasting. In the days before, though, keep a normal diet with your usual carbohydrates.

Is one high value enough for the diagnosis? Yes: with the 75 g load, a single value at or above the threshold is enough to diagnose gestational diabetes.

Screening at home

Rima GlucoLens lets you run a urine glucose screen simply and non-invasively, at home, and the app helps interpret the result. It remains a screening tool: the diagnosis of gestational diabetes rests with the OGTT and the doctor.

References: World Health Organization (WHO); American Diabetes Association (ADA); IADPSG criteria for the OGTT in pregnancy. This article is for information only and does not replace medical advice.

Last updated: July 2026