Being asked to test your blood sugar (also called blood glucose) levels can feel overwhelming at first.
You may be wondering:
- Am I doing this right?
- What do these numbers actually mean?
- What happens if they’re too high — or too low?
This is completely normal.
Blood sugar testing is not about being perfect — it’s about understanding how your body responds during pregnancy so you and your maternity team can keep both you and your baby safe.
Understanding your gestational diabetes blood sugar levels can help you feel more confident and in control during pregnancy.
This page will guide you through:
✔ What your blood sugar levels should be
✔ When to test
✔ What your readings mean
✔ What to do if your numbers are higher or lower than expected
If you’ve recently been diagnosed, you may also find it helpful to read our guide to gestational diabetes diagnosis.
What should my blood sugar levels be?
Most women with gestational diabetes are advised to aim for fasting levels below around 5.3 mmol/L and post-meal levels below around 7.8 mmol/L (1 hour) or 6.4 mmol/L (2 hours), depending on local guidance.
Blood sugar targets can differ slightly depending on where you live in the UK and which guidance your maternity service follows.
In England, Wales and Northern Ireland, many teams follow NICE guidance. In Scotland, services may follow SIGN guidance. Your own hospital or Health Board may also set individual targets for you.
Always follow the targets given by your own diabetes team.
These targets are based on national clinical guidelines used across the NHS.
NICE blood sugar targets
NICE advises pregnant women with any form of diabetes, including gestational diabetes, to keep capillary plasma glucose below these target levels, if this can be achieved without problematic hypoglycaemia:
| Time of test | NICE target |
|---|---|
| Fasting | below 5.3 mmol/L |
| 1 hour after meals | below 7.8 mmol/L |
| 2 hours after meals | below 6.4 mmol/L |
NICE also advises pregnant women with diabetes who are taking insulin to keep capillary plasma glucose above 4.0 mmol/L.
SIGN blood sugar targets
SIGN 171 recommends the following glucose targets for women with type 1, type 2 and gestational diabetes:
| Time of test | SIGN target |
|---|---|
| Fasting | below 5.5 mmol/L |
| 1 hour after meals | below 8.0 mmol/L |
| 2 hours after meals | below 7.0 mmol/L |
SIGN 171 also updated Scottish diagnostic OGTT thresholds for gestational diabetes to: fasting plasma glucose ≥5.3 mmol/L, one-hour post 75g oral glucose load ≥10.6 mmol/L where used, or two-hour post 75g oral glucose load ≥9.0 mmol/L.
When should I test my blood sugar?
Your diabetes team will advise you when and how often to test your blood sugar.
Most people with gestational diabetes are asked to test several times a day to build a clear picture of how their levels change.
Typical testing times
You will usually be asked to test:
- Fasting – as soon as you wake up, before eating or drinking anything
- After meals – usually 1 hour after starting your meal
- Sometimes additional checks, depending on your care
Some diabetes care teams may ask you to test:
- 2 hours after meals instead of 1 hour, or
- Before meals (pre-meal testing) rather than after meals
This depends on local guidelines and your individual care plan.
First bite or last bite – when should you start timing?
One of the most common questions about post-meal testing is whether the clock should start from your first bite or when you finish eating.
Different diabetes teams give different instructions, and current UK guidance does not clearly define which to use.
Try to test at the same times each day so your readings are consistent and easier to compare.
Why timing matters
The timing of your test affects your result.
For example:
- Testing too early after a meal may miss the peak in your blood sugar
- Testing too late may not reflect how your body responded to that meal
Keeping your testing times consistent helps your care team understand your results more accurately.
Do I need to test every day?
Many people are asked to test their blood sugar daily, especially in the early stages after diagnosis.
In some cases, your team may adjust how often you test depending on:
- Your blood sugar levels
- Whether your levels are stable
- Your treatment plan
Always follow the advice given by your own diabetes team.
One of the key readings you’ll be asked to take is your fasting blood sugar. This is usually the first test of the day, and understanding what it means can help you get the most accurate results.
What does fasting mean?
Fasting blood sugar is your blood glucose level when you have not eaten or had anything to drink (except water) for several hours.
For most people, this means testing first thing in the morning, as soon as you wake up, before eating or drinking anything.
This is sometimes called your overnight fasting level.
Test your fasting blood sugar as soon as you wake up, before eating or drinking anything (except water).
Why fasting levels matter
Your fasting reading shows how your body manages blood sugar overnight, without the influence of food.
It can sometimes be higher than expected and is often the most difficult reading to control. This is because it is influenced by pregnancy hormones, not just what you eat.
Many women find their fasting reading is the most frustrating — this is very common in gestational diabetes.
Your fasting level is often the hardest number to influence, and your care team understands this.
Common mistakes when testing fasting blood sugar
When you’re new to testing, it’s easy for small things to affect your results without realising. Some common issues include:
- Testing after getting up and moving around for a while
- Having a drink other than water before testing
- Testing after eating or drinking overnight
- Waiting too long after waking up
These are very common, especially when you’re still getting used to testing.
For the most accurate result, test as soon as you wake up, before eating or drinking anything.
Fasting is one of the key times you’ll be asked to test your blood sugar. Understanding what it means can help you get the most accurate readings.
What your blood sugar readings mean
It’s easy to feel worried when a number is outside your target range.
But one reading on its own doesn’t tell the whole story.
What matters more is:
- Patterns over time
- Whether your levels are consistently higher or lower than expected
- How your body responds to different meals
Your readings are there to give you information — not to judge you.
Blood sugar levels can vary from day to day, even if you eat similar foods.
This is because gestational diabetes is influenced by pregnancy hormones and many other factors, as well as diet.
Many people notice that certain meals or times of day affect their readings more than others. This is completely normal.
Over time, your readings help you and your maternity team understand what is working and whether any changes are needed.
If your readings are outside your target range, it can help to know what to do next.
What to do if your blood sugar is higher than expected
Seeing a higher reading can feel worrying, especially at the start.
But it’s important to remember that one reading on its own doesn’t tell the whole story.
A single high reading is not unusual and does not mean you’ve done anything wrong.
If you have one higher reading
- Try not to panic
- Think about what you ate and when
- Continue testing as normal
Occasional higher readings can happen, even when you are doing everything “right”. They are completely normal and to be expected.
If your readings are regularly higher than your target
- Look for patterns (for example, after certain meals or at certain times of day)
- Consider whether food choices or portion sizes may be affecting your levels
- Keep testing as advised
If your readings continue to be above your target, speak to your diabetes team.
They may:
- Offer more specific dietary guidance
- Suggest changes to your care plan
- Recommend medication if needed
You are not expected to keep every reading within range. What matters most is the overall pattern of your results.
When should I contact my diabetes care team?
You should contact your team if:
- Your fasting levels are consistently above your target
- You are having repeated high readings after meals
- You are unsure what to do or feel worried about your results
Your team is there to support you, not judge you. Asking for help early can make things much easier to manage.
Occasionally, blood sugar levels can also be lower than expected. Knowing how to manage this can help you feel more confident.
What to do if your blood sugar is lower than expected
Low blood sugar (sometimes called a hypo) is less common in gestational diabetes, but it can happen — particularly if you are taking medication such as insulin.
A low reading is usually considered to be:
Below 4.0 mmol/L
Signs your blood sugar may be low
- Feeling shaky or weak
- Dizziness or lightheadedness
- Sweating
- Hunger
- Feeling anxious or irritable
Sometimes symptoms can be mild or not obvious at first, which is why testing your blood sugar levels when experiencing any of these symptoms is important.
What to do if your blood sugar is low
First: are you taking insulin?
This is important, because how you treat a low reading can differ.
If you are taking insulin:
Treat this as a hypo:
Have 15–20g of fast-acting glucose, such as:
- A small glass of fruit juice
- A full-sugar drink (not diet)
- Glucose tablets
- Sweets such as jelly babies
Wait 10–15 minutes, then test your blood sugar again. If your levels are still below 4.0 mmol/L:
- Repeat the treatment
- Wait 10–15 minutes
- Test again
Once your blood sugar has risen:
Have something to eat, such as a snack or your next meal, to help keep your levels stable.
If you are not taking insulin
A low reading can sometimes happen, but it is usually less serious.
- Have something to eat
- Choose a balanced (GD-friendly) snack or your next meal
- Continue testing as normal
Your blood sugar levels should return to your normal range.
If your blood sugar drops below 3.0 mmol/L or you feel unwell, seek medical advice.
Low readings are less common in gestational diabetes, but knowing how to manage them can help you feel more confident.
When to seek advice
Speak to your maternity or diabetes team if:
- Your blood sugar remains below 4.0 mmol/L
- You are having repeated low readings
- You feel unwell or symptoms don’t improve
If you are taking medication, your treatment may need adjusting.
Low blood sugar can feel unpleasant, but it can usually be managed quickly once you know what to do.
If you’re finding your readings are higher than expected, what you eat can make a significant difference.
More support and guidance
If you want more detailed guidance on managing your blood sugar levels, these pages can help:
→ What to do if you’re struggling with high fasting blood sugar levels
→ What to do if your blood sugar is high
→ Understanding low blood sugar, hypos and false hypos
This information is based on current UK clinical guidance and is designed to support, not replace, advice from your own maternity team.