Glucose tests are done at different times depending on the reason for testing, but the most commonly asked one (in pregnancy) is usually done between 24 and 28 weeks of pregnancy, and earlier if you have risk factors for diabetes.

Key situations when glucose tests are done

1. During pregnancy (gestational diabetes screen)

Most people asking “when is glucose test done” are referring to the routine pregnancy test.

  • A screening glucose test (glucose challenge test) is usually done at 24–28 weeks of pregnancy.
  • It may be done earlier in pregnancy if you have risk factors such as obesity, history of gestational diabetes, prior large baby, family history of diabetes, PCOS, or high blood pressure.
  • If the screening is high, you’re asked to do a longer oral glucose tolerance test (OGTT) on another day to confirm the diagnosis.

📝 Tiny example: Someone at 26 weeks with no risk factors will typically be booked for the 1‑hour glucose drink test. If that comes back high, they return for a 3‑hour OGTT.

2. General diabetes screening (not pregnant)

Doctors use blood glucose tests to screen for or diagnose diabetes and prediabetes in adults.

  • A fasting blood glucose test is done after not eating for at least 8 hours , often first thing in the morning.
  • An oral glucose tolerance test (OGTT) is usually done in the morning after an overnight fast , with blood draws before and then 1–2 (sometimes 3) hours after drinking a glucose solution.
  • A random blood glucose test can be done at any time of day , especially if you have symptoms like excessive thirst, frequent urination, or unexplained weight loss.

3. If you already have diabetes

If you already have diabetes, “when is glucose test done” usually means home glucose checks or continuous monitoring.

  • With type 1 diabetes , blood sugar may be checked 4–10 times a day : before meals and snacks, sometimes after meals, before and after exercise, before bed, and more often when sick or adjusting medicines.
  • With type 2 diabetes using insulin , checks are often done before meals and at bedtime , and sometimes less often if on long‑acting insulin only.
  • Some people use a continuous glucose monitor (CGM) that tracks levels throughout the day and night, so you see trends instead of single points.

Simple HTML table of typical timings

html

<table>
  <tr>
    <th>Situation</th>
    <th>Type of glucose test</th>
    <th>When it’s usually done</th>
  </tr>
  <tr>
    <td>Routine pregnancy (no major risk factors)</td>
    <td>Glucose screening / challenge test</td>
    <td>Between 24–28 weeks of pregnancy[web:3][web:9]</td>
  </tr>
  <tr>
    <td>High‑risk pregnancy (e.g., obesity, prior GDM)</td>
    <td>Glucose screening ± OGTT</td>
    <td>May be done earlier than 24 weeks, then repeated as needed[web:3][web:9]</td>
  </tr>
  <tr>
    <td>General diabetes screening (not pregnant)</td>
    <td>Fasting blood glucose</td>
    <td>Morning after at least 8 hours of fasting[web:5][web:7]</td>
  </tr>
  <tr>
    <td>Diagnosis of diabetes / prediabetes</td>
    <td>Oral glucose tolerance test (OGTT)</td>
    <td>Morning after overnight fast, with repeated blood draws over 2–3 hours[web:5][web:8]</td>
  </tr>
  <tr>
    <td>Symptoms of diabetes (thirst, urination, fatigue)</td>
    <td>Random blood glucose test</td>
    <td>Any time of day, no fasting needed[web:7]</td>
  </tr>
  <tr>
    <td>Known type 1 diabetes</td>
    <td>Home capillary blood glucose/CGM</td>
    <td>Multiple times daily: before meals/snacks, exercise, bed, and when sick[web:1]</td>
  </tr>
  <tr>
    <td>Known type 2 diabetes on insulin</td>
    <td>Home capillary blood glucose/CGM</td>
    <td>Often before meals and at bedtime, adjusted to insulin regimen[web:1]</td>
  </tr>
</table>

Mini “forum style” note

“My OB booked my first glucose test right around 26 weeks, but because I had PCOS they checked me once early in the second trimester too. The timing can vary, so always go with what your own doctor recommends.”

TL;DR:

  • Pregnancy screening: usually 24–28 weeks , earlier if you’re high‑risk.
  • General diabetes check: fasting or OGTT are done after an overnight fast, usually in the morning.
  • Existing diabetes: glucose is checked multiple times per day or continuously depending on your treatment.

Information gathered from public forums or data available on the internet and portrayed here.