pregnancy-birth

Gestational Diabetes: Screening, Numbers, Treatment, and What Happens After

By Dr. Adeeb Alshahrour · January 27, 2023

Gestational diabetes is high blood sugar first recognised in pregnancy. It affects somewhere around 8 to 10 percent of pregnancies in the United States, and the number has been rising.

The mechanism is not a failure of willpower. From roughly the middle of pregnancy, the placenta produces hormones — human placental lactogen, progesterone, cortisol — that deliberately blunt the mother's response to insulin so that more glucose stays in the bloodstream and reaches the baby. Every pregnancy becomes insulin-resistant. Gestational diabetes is what happens when the pancreas cannot raise its insulin output enough to keep pace.

That distinction matters, because the treatment is not punishment and the diagnosis is not a verdict on how you have eaten. It is a metabolic stress test that pregnancy applies to everyone, and it reveals something about your pancreas that was true before you were pregnant.

Symptoms — there usually aren't any

Thirst, frequent urination, and fatigue are all normal in pregnancy anyway, which makes them useless as signals. Gestational diabetes is almost always silent. This is precisely why it is screened for rather than waited for, and why the screening happens in every pregnancy regardless of weight, age, or family history.

When screening happens

All pregnant patients are screened at 24 to 28 weeks. That window is chosen because it is late enough for placental insulin resistance to have developed, and early enough that treatment has months to work.

Screening happens earlier — at the first prenatal visit — if you have risk factors, because some of what turns up early is actually undiagnosed type 2 diabetes that predates the pregnancy. Early testing is recommended with:

A BMI of 30 or above, or 25 and above with an additional risk factor
Gestational diabetes in a previous pregnancy — the recurrence rate is high
A first-degree relative with diabetes
**Polycystic ovary syndrome**, which shares the underlying insulin resistance
A previous baby weighing 4,000 g (about 9 lb) or more
Prediabetes, or a previously elevated A1C
Chronic hypertension, or a history of cardiovascular disease
Ancestry associated with higher risk, including South Asian, Middle Eastern, Hispanic, African American, Native American, and Pacific Islander

If early screening is normal, it is repeated at 24 to 28 weeks. Early normal does not mean exempt.

The 1-step and 2-step approaches

There are two accepted ways to test, and they use different numbers. Know which one you are having, because a "high" result on one is not the same finding as a "high" on the other.

The 2-step approach

This is what ACOG continues to recommend, and it is what most US practices use.

Step one: the 50-gram glucose challenge. You drink a sweet glucose solution and have blood drawn one hour later. No fasting required — you can eat beforehand. A result at or above the practice's cut-off (130, 135, or 140 mg/dL, depending on the lab) means you go on to step two. This is a screen, not a diagnosis, and most people who screen positive do not have gestational diabetes.
Step two: the 100-gram, 3-hour oral glucose tolerance test. This one requires an overnight fast. Blood is drawn fasting, then at one, two, and three hours. Using the Carpenter-Coustan thresholds, the values are fasting 95, 1-hour 180, 2-hour 155, and 3-hour 140 mg/dL. Two or more values at or above threshold makes the diagnosis.

The 1-step approach

Endorsed by the American Diabetes Association and used by many practices internationally. A single 75-gram, 2-hour test after an overnight fast, with blood drawn fasting, at one hour, and at two hours. Thresholds are fasting 92, 1-hour 180, 2-hour 153 mg/dL, and one value at or above threshold makes the diagnosis.

The 1-step approach diagnoses considerably more people — it roughly doubles the diagnosis rate. Large trials have not shown that the extra diagnoses translate into clearly better outcomes for mothers and babies, which is why ACOG has not adopted it as the single standard. Either approach is defensible; consistency within a practice matters more than which one is chosen.

A note on the drink: it is unpleasant, and vomiting it means the test has to be repeated. Ask about it beforehand rather than skipping the test. Missing a diagnosis is far worse than an unpleasant morning.

What the diagnosis actually means

Untreated, sustained high maternal glucose crosses the placenta, the baby's pancreas responds with extra insulin, and insulin is a growth hormone. The consequences worth naming:

Macrosomia — a baby measuring large for gestational age, which raises the risk of shoulder dystocia, birth injury, and caesarean delivery
Neonatal hypoglycaemia — after birth the glucose supply stops abruptly but the baby's high insulin output does not, so blood sugars are checked in the first hours
Preeclampsia and gestational hypertension, which are more common with gestational diabetes
Preterm birth, and neonatal jaundice and breathing difficulty
Stillbirth, at the severe and uncontrolled end
Polyhydramnios — excess amniotic fluid

Here is the important half of that list: treatment reduces these risks substantially, and it works. Randomised trials of treating gestational diabetes show clear reductions in macrosomia, shoulder dystocia, and hypertensive complications. A treated, well-controlled pregnancy with gestational diabetes usually looks like any other pregnancy.

Treatment: diet and monitoring first

Roughly 70 to 85 percent of people with gestational diabetes reach target on nutrition and activity alone. Medication is not the first step, and needing it later is not a failure.

Monitoring

You will check your blood sugar with a fingerstick meter, typically four times a day: fasting on waking, and after each meal. The standard targets are:

Fasting: below 95 mg/dL
1 hour after the start of a meal: below 140 mg/dL
2 hours after the start of a meal: below 120 mg/dL

Pick one post-meal time and stick with it. Record every reading with what you ate — the log is the diagnostic tool, and a pattern of one bad number after the same breakfast is actionable in a way that a general sense of "it's been high" is not.

Nutrition

Referral to a registered dietitian is standard and worth taking up. The broad principles:

Carbohydrate is not banned — it is distributed. Roughly 40 to 50 percent of calories from carbohydrate, spread across three moderate meals and two to three snacks rather than concentrated in one or two large meals.
Pair carbohydrate with protein or fat every time. Toast alone spikes; toast with eggs does not.
Breakfast is the hardest meal. Insulin resistance peaks in the early morning, and cereal, juice, and fruit-heavy breakfasts are the most common cause of a single stubborn high reading. Breakfast usually needs the lowest carbohydrate of the day.
Choose slow carbohydrates — whole grains, legumes, vegetables, whole fruit — over juice, sweetened drinks, and refined starch.
Do not skip meals or drastically restrict. Starvation ketosis is a real risk in pregnancy and is not a strategy.

Activity

Walking for 20 to 30 minutes after meals is the single highest-yield habit here. Muscle takes up glucose without needing insulin, and a post-meal walk often moves a stubborn 1-hour reading into range on its own.

When medication is needed

If readings stay above target — commonly defined as a meaningful proportion of values out of range over one to two weeks — medication is added.

Insulin is the preferred first-line medication. It does not cross the placenta, it can be adjusted precisely to the specific readings that are high, and it has the longest safety record in pregnancy. It is injected, usually with a fine pen needle, and the fear of it is almost always worse than the reality.
Metformin is a reasonable alternative for patients who decline insulin, cannot safely manage injections, or cannot afford insulin. It does cross the placenta, long-term child outcome data are still accumulating, and a substantial proportion of patients on metformin eventually need insulin added anyway. It is not superior to insulin, and patients should be told so.
Glyburide is no longer recommended as a first-line agent. It performs less well than either insulin or metformin on macrosomia and neonatal hypoglycaemia.

Requiring medication does not mean you did the diet wrong. Some pancreases cannot meet the demand of a third-trimester placenta no matter what is on the plate.

Extra monitoring in pregnancy

Growth ultrasounds in the third trimester to track fetal size and amniotic fluid
Antenatal fetal testing — non-stress tests or biophysical profiles, typically from around 32 weeks for anyone on medication or with poor control, and often later for diet-controlled diabetes
Blood pressure and urine protein at every visit, because preeclampsia risk is higher
A baseline eye and kidney check if the picture suggests pre-existing type 2 diabetes rather than true gestational diabetes

Delivery

Gestational diabetes is not, by itself, a reason for a caesarean.

Diet-controlled and well-controlled: there is no reason to deliver early. Expectant management to 39+0 to 40+6 weeks is appropriate.
Medication-controlled and well-controlled: delivery is generally planned at 39+0 to 39+6 weeks.
Poorly controlled, or with other complications: earlier delivery may be recommended, individually decided.
Estimated fetal weight of 4,500 g or more: a conversation about planned caesarean is warranted, because the risk of shoulder dystocia rises steeply. Ultrasound estimates of fetal weight carry meaningful error, and that uncertainty is part of the discussion.

In labour, blood glucose is monitored and insulin requirements usually fall away almost immediately after the placenta is delivered. Most people with gestational diabetes stop all medication at birth. The baby's blood sugar is checked in the first hours and early feeding is encouraged. See labor and delivery for how a delivery plan is built.

After the birth — the appointment people skip

Gestational diabetes resolves at delivery. The underlying tendency does not.

Have a 75-gram, 2-hour oral glucose tolerance test at 4 to 12 weeks postpartum. Not an A1C, which is unreliable soon after pregnancy, and not a casual fasting sugar. This is the test that distinguishes a genuine return to normal from prediabetes or type 2 diabetes that has simply carried on.

After that, repeat testing every one to three years for life. The reason is blunt: up to half of people who had gestational diabetes develop type 2 diabetes within 10 years, and the risk never returns to baseline. This is also the moment where it is most preventable — sustained modest weight loss and regular activity cut progression to type 2 diabetes substantially, and metformin is an option for some.

Two more things that belong in the same conversation:

Breastfeeding lowers your risk of later type 2 diabetes and helps stabilise the baby's blood sugar. Support for it is part of postpartum care.
Gestational diabetes is also a cardiovascular risk marker. Blood pressure and lipids deserve attention at routine visits from now on, not in twenty years. Bring it up at your annual check-up and make sure it is in your chart.

Plan the next pregnancy with this in mind: aim to start at a healthy weight, and expect early screening rather than waiting until 24 weeks.

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Medical disclaimer

This article is general health information, not medical advice for any individual. Glucose targets and medication decisions must be set by the clinician managing your pregnancy. Contact your obstetrician promptly for readings persistently above target, ketones on testing, severe headache or visual changes, or a noticeable decrease in fetal movement. In an emergency, call 911.