Gestational diabetes mellitus (GDM) is one of the most common medical complications of pregnancy, affecting up to 10% of pregnancies in the United States. Routine screening between 24 and 28 weeks of gestation helps identify women whose bodies cannot produce enough insulin to meet the increased demands of pregnancy. Interpreting your GDM screening results correctly empowers you to take the right steps for yourself and your baby. This guide explains what the numbers mean, how to review your own readings at home, and how to have a productive conversation with your healthcare provider.

Understanding GDM Screening Tests

Two main approaches are used to screen for gestational diabetes: the one-step and the two-step method. The American College of Obstetricians and Gynecologists (ACOG) and the American Diabetes Association (ADA) both endorse screening, but they differ slightly in their protocols. Knowing which test you had is the first step to interpreting your results.

The One-Step Oral Glucose Tolerance Test (OGTT)

The one-step 75-gram OGTT is more common in many parts of the world and is recommended by the ADA. You will be asked to fast for at least 8 hours overnight. A fasting blood sample is drawn, then you drink a 75-gram glucose solution. Blood samples are taken again at 1 hour and 2 hours after the drink. A diagnosis of GDM is made if any one of the following thresholds is met or exceeded:

  • Fasting: 92 mg/dL (5.1 mmol/L) or higher
  • 1-hour: 180 mg/dL (10.0 mmol/L) or higher
  • 2-hour: 153 mg/dL (8.5 mmol/L) or higher

These cutoffs are based on data from the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study, which linked even mild glucose elevations to increased risks of large-for-gestational-age infants, cesarean delivery, and neonatal hypoglycemia.

The Two-Step Approach (Common in the U.S.)

ACOG recommends a two-step process. First, a non-fasting 50-gram glucose challenge test (GCT) is given. A blood sample is drawn 1 hour later. If the result is 130–140 mg/dL or higher (depending on your lab’s cutoff), a second step is performed: a 100-gram OGTT. That fasting test measures blood glucose at fasting, 1 hour, 2 hours, and 3 hours. GDM is diagnosed if two or more of the following Carpenter-Coustan criteria are met or exceeded:

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

Some laboratories use the National Diabetes Data Group (NDDG) criteria, which have slightly higher cutoffs. Ask your provider which criteria your lab uses so you can compare apples to apples.

Interpreting Your Screening Results at Home

If you have received a copy of your lab report or have a home glucose monitor (often prescribed after a diagnosis), you can start reviewing numbers on your own. Keep in mind that home glucometer readings are finger-stick capillary measurements, while lab results are venous plasma measurements. The numbers may differ slightly, but the trends are reliable. Here is how to make sense of them.

Reading Your Lab Report

Look at the reference range column on your report. It will show the normal values for each time point. Compare your results against those ranges. For a 1-hour screening test (50 g), a result above 140 mg/dL (or 130 mg/dL at some centers) is considered abnormal and requires follow-up testing. For a diagnostic 3-hour test, pay attention to how many of the four values are elevated. Remember: in the two-step method, one abnormal value is not diagnostic; two or more are needed for a GDM diagnosis.

Using a Home Glucose Monitor After Diagnosis

If you have been diagnosed with GDM, your provider will likely ask you to check your blood sugar four times a day: fasting (when you wake up, before eating) and then 1 or 2 hours after each meal. The target ranges are typically:

  • Fasting: Less than 95 mg/dL
  • 1 hour after a meal: Less than 140 mg/dL (or 130 mg/dL in some practices)
  • 2 hours after a meal: Less than 120 mg/dL

Write down every reading in a log (or use a smartphone app). Look for patterns: Is your fasting number always high? Are certain meals (especially those with carbohydrates) causing spikes? A log gives you and your doctor actionable data to adjust diet, exercise, or medication.

What Abnormal Readings Mean

A single high reading is not a crisis, but repeated elevations above targets indicate that your diabetes management needs adjustment. For example, elevated fasting levels often mean your liver is releasing too much glucose overnight, which may require a bedtime snack adjustment or medication. Post-meal spikes suggest the meal had too many carbs or not enough protein, or that you need more physical activity after eating. A pattern of high readings for several days warrants a call to your doctor.

Risk Factors and Why Early Interpretation Matters

Understanding your screening results is especially important if you have any of these risk factors for GDM:

  • Body mass index (BMI) of 30 or higher before pregnancy
  • Previous pregnancy with GDM
  • Family history of type 2 diabetes (parent or sibling)
  • Polycystic ovary syndrome (PCOS)
  • Previous baby weighing more than 9 pounds (4 kg)
  • Being Hispanic, Black, Native American, South Asian, or Pacific Islander (higher prevalence)

If your screening results are borderline, early interpretation can trigger lifestyle interventions that reduce your risk of developing GDM later in pregnancy. Even a single elevated value in the 1-hour challenge test may indicate impaired glucose tolerance, and some providers will recommend dietary changes even if the formal diagnostic criteria are not met. Read more about risk factors at the CDC’s gestational diabetes page.

Discussing Results with Your Doctor

Your prenatal visit is the ideal setting to review your screening results in context. The doctor will not look at numbers in isolation—they will consider your medical history, weight gain, blood pressure, and any symptoms like excessive thirst or frequent urination. Here is what to expect during that conversation.

Preparing for the Appointment

Bring a copy of your lab report and any home glucose logs. Write down questions ahead of time so you don’t forget. If you received an abnormal screening result, you may be referred to a maternal-fetal medicine specialist or a diabetes educator. In that case, ask your primary obstetric provider what to expect from those consultations.

Questions to Ask Your Doctor

  • What do my specific numbers indicate about my risk?
  • Do I need to start checking blood sugar at home? What meter do you recommend?
  • What are my target blood sugar ranges?
  • Should I see a registered dietitian or diabetes educator?
  • If my numbers do not improve with diet and exercise, what medication options are available? Are there risks for the baby?
  • How will GDM affect my delivery plan? Will I need extra fetal monitoring?
  • What about after birth? Do I need a postpartum glucose tolerance test?

Another critical question: “What numbers should prompt me to call you right away?” Many providers want to know if fasting readings consistently exceed 110 mg/dL or if post-meal readings go above 200 mg/dL. Having a clear threshold helps you act decisively.

Understanding Your Doctor’s Management Plan

If you are diagnosed with GDM, your doctor will outline a plan that typically includes:

  • Medical nutrition therapy: A specific carbohydrate-controlled diet, often with three small meals and two to three snacks. A dietitian can help you count carbs and choose low-glycemic foods.
  • Physical activity: Moderate exercise for 20–30 minutes most days, such as walking, swimming, or stationary cycling. Exercise improves insulin sensitivity.
  • Blood glucose monitoring: Typically four times daily, as described above.
  • Medication if needed: Metformin (oral) or insulin injections if targets are not met after two weeks of diet and exercise. Insulin is the gold standard because it does not cross the placenta.

Your doctor will also schedule more frequent ultrasounds to check fetal growth and may recommend nonstress tests or biophysical profiles in the third trimester. For a deeper look at management strategies, see these clinical guidelines from the National Library of Medicine.

Managing GDM at Home: Practical Tips

Taking ownership of your daily numbers gives you confidence. Here are evidence-based strategies to keep your readings in range.

Carbohydrate Timing and Portion Control

Spread your carbohydrate intake evenly across the day. Avoid eating more than 30–45 grams of carbs at a meal and 15–30 grams at a snack. Prioritize complex carbohydrates like whole grains, legumes, and vegetables over refined sugars and white flour. Pair carbs with protein and healthy fats—for example, an apple with peanut butter, or a whole-wheat cracker with cheese.

The Role of Physical Activity

Walking after meals is one of the most effective ways to lower postprandial blood sugar. A brisk 10–15 minute walk can reduce glucose levels by 15–20 mg/dL on average. If you are on bed rest or have limitations, upper body exercises or seated stretches can still help. Always check with your obstetrician before starting a new exercise routine.

Fasting Hyperglycemia

If your morning fasting readings are high despite a good bedtime snack, try a different snack composition. Options include a protein-rich snack (e.g., a hard-boiled egg and a few almonds) or a snack with a small amount of complex carbohydrate (e.g., half a slice of whole-grain toast with avocado). Avoid skipping snacks, as a prolonged fast can trigger the liver to release stored glucose (the dawn phenomenon).

Some continuous glucose monitors (CGMs) are now approved for use during pregnancy. A CGM provides real-time data without finger sticks and can alert you to highs and lows. Discuss with your insurance and doctor whether a CGM is covered for GDM. Even a simple logbook can reveal patterns—for instance, if your 2-hour values are always high after breakfast, you might need to reduce the breakfast carb portion or walk for 10 minutes afterward.

When to Contact Your Doctor

While most GDM can be managed at home, certain situations require immediate medical attention. Call your provider if:

  • Your blood sugar > 200 mg/dL for more than two consecutive readings
  • You experience symptoms of hypoglycemia (shakiness, sweating, confusion, blurred vision) and your glucose is < 60 mg/dL
  • You cannot keep food or fluids down due to nausea or vomiting
  • You notice decreased fetal movement
  • You have signs of urinary tract infection or vaginal infection (frequency, burning, discharge)
  • You develop blurred vision, severe headache, or swelling in your hands/face (possible signs of preeclampsia, which is more common with GDM)

It is always better to call and be reassured than to wait and worry.

Postpartum Follow-Up and Long-Term Implications

GDM usually resolves after delivery, but it raises your risk of developing type 2 diabetes later in life. Approximately 50% of women with GDM will develop type 2 diabetes within 5–10 years. That is why interpreting your results does not end at birth. Your doctor should schedule a 75-gram OGTT at 4–12 weeks postpartum to confirm that your glucose tolerance has returned to normal. The American Diabetes Association recommends follow-up testing every 1–3 years after that. Women with a history of GDM also benefit from lifestyle interventions such as the National Diabetes Prevention Program to reduce their risk.

Learn about postpartum diabetes prevention at the American Diabetes Association’s gestational diabetes resource. Another excellent reference is the NIDDK guide on GDM.

Putting It All Together

Interpreting GDM screening results is a partnership between you and your healthcare team. Start by understanding which test you took and the specific thresholds used. At home, use your glucose log to spot patterns and adjust your diet and activity accordingly. When you meet with your doctor, bring your data and ask focused questions. Remember that a diagnosis of GDM is not a failure—it is a signal to take extra care. With proper management, the vast majority of women with gestational diabetes deliver healthy babies and return to normal glucose levels postpartum. Stay proactive, stay informed, and trust the process.