In this post, we are going to discuss blood sugar levels, test times, targets, spikes in blood sugar levels and spike testing; a tool that many have found useful in managing gestational diabetes and diabetes in pregnancy.

Blood sugar levels are constantly changing. A spike in blood sugar levels is the highest peak your blood sugar levels reach after eating or drinking. A good way to show how blood sugar levels change visually is via an image from a Freestyle Libre continual blood glucose monitoring system:


When we eat or drink, the carbs from those foods/drinks convert into glucose in the bloodstream

Macronutrients impact on blood glucose

When blood sugar levels spike, this sends a signal in our body to process the glucose, using insulin to break it down into our cells and convert it into energy. However, with gestational diabetes, we can not do this as well as we normally would. This means that we can end up having higher blood sugar levels than we should which in turn can cause complications in the pregnancy.

How do high blood sugar levels impact the baby?

With gestational diabetes, when there is too much sugar in the mother’s bloodstream, this is passed through or ‘fed’ to the baby. The baby then has to increase its own insulin production to help process the excess sugars. Insulin is a growth hormone and the result is that the baby grows excessively and for many the AC [abdominal circumference] increases. It is adipose tissue (subcutaneous fat) caused by the overproduction of insulin that causes the baby to grow ‘big’.

Controlling blood sugars with diet, exercise and some will also need meds/insulin, this helps the baby to regulate their insulin production to normal levels and the rate of growth of the baby’s AC slows whilst the rest of the baby’s growth catches up. This means that the baby returns to ‘normal’ or average growth size.

There has been uncertainty if it is the overall glucose control or the spikes in blood sugar levels that influence the baby’s growth but the HAPO (Hyperglycemia and Adverse Pregnancy Outcomes) study​1​ found that both fasting and postprandial glucose levels influence fetal growth and so this is why the majority of ladies will be advised to test both fasting levels and postprandial [post meal] levels.

Optimal glucose control before pregnancy reduces congenital malformations and miscarriage, while during pregnancy it reduces macrosomia, stillbirth, neonatal hypoglycaemia, and respiratory distress syndrome.​2​

large growth

Test times and targets for monitoring blood sugar levels

Although there are National guidelines with recommendations that are backed by research as to what blood sugar targets should be used for the best outcomes with gestational diabetes, hospitals and Trusts do not have to follow them.

This means that ladies in the UK & Ireland can be given all sorts of different blood glucose monitoring targets and test times. Some may be very strict, others can be very lenient. You could literally go to one hospital and be given one set of targets and test times and the next hospital a few miles away could be dramatically different.

From multiple tests per day before and after all meals and before bed, to only being tested at a breakfast club after being given a specific high-carb load breakfast, there are so many different testing regimes given to women diagnosed with gestational diabetes!

When do you test your blood sugar levels?

Here is what we found from 1,222 women with gestational diabetes which blood testing regime were they advised to follow:

Testing BMs
Testing fasting levels

Are the test times you’ve been given going to help you enough?

One question to ask yourself is “are the test times and targets you’ve been given going to help you manage your gestational diabetes the best you possibly can?”

If you have only been asked to test your blood sugar levels before all meals one day and after all meals the next, is this giving you enough information to be able to understand how and where to adjust your diet to achieve the best possible blood sugar levels?

Likewise, if you have only been asked to monitor your blood sugar levels once a week, is this going to be sufficient enough for you to see what’s happening and your tolerance to different foods? Or does it encourage you to follow a strict diet on the day you know you’re testing on and to be less strict when you know you are not testing?

National guidelines for testing

NICE Guidelines for testing​3​

1.3.5 Advise pregnant women with any form of diabetes to maintain their capillary plasma glucose below the following target levels, if these are achievable without causing problematic hypoglycaemia:
fasting: 5.3 mmol/litre and
1 hour after meals: 7.8 mmol/litre or
2 hours after meals: 6.4 mmol/litre. [new 2015]

1.3.6 Advise pregnant women with diabetes who are on insulin or glibenclamide to maintain their capillary plasma glucose level above 4 mmol/litre. [new 2015]

NICE Guidelines NG3 Diabetes in Pregnancy

SIGN Guidelines for testing​2​

Postprandial glucose monitoring should be carried out in pregnant women with gestational diabetes and may be considered in pregnant women with type 1 or 2 diabetes.

…aim to achieve blood glucose: between 4 and 6 mmol/l preprandially, and <8 mmol/l one hour postprandially, or <7 mmol/l two hours postprandially >6 mmol/l before bed.


HSE Guidelines for testing​4​

5.3.6 Blood glucose targets during pregnancy

The following target values are recommended for optimum maternal and fetal outcome: – Fasting capillary glucose level: 3.5-5.0mmol/L – 1 hour post-prandial capillary glucose level: <7.0mmol/L

HSE Guidelines for the management of GDM

It is worth noting that not one National guideline recommends only preprandial (pre-meal) testing, or alternative days of preprandial and postprandial testing. They all recommend fasting and postprandial testing, with additional preprandial testing recommended for those using insulin therapy

One hour postprandial testing versus two hours

Many studies have shown that post-prandial hyperglycaemia is a predictor for fetal macrosomia and may contribute to neonatal hypoglycaemia. Current recommendations state that tests should be performed at either one or two hours post meals. Studies have demonstrated, however, that

the 1hour post prandial test is more likely to detect abnormal values which may require treatment and helps the person understand the relationship between food and blood glucose levels​3,5​

NICE Guidelines NG3 Diabetes in Pregnancy

Depending on your test times, you may be missing the spike in your blood sugar levels

To show the difference between one hour versus two hours of postprandial testing, here is an image of a mother’s test results. This GD mother was concerned that the 2hr postprandial testing she was doing was causing her to miss spikes in her blood sugar levels and so she decided to start testing at both 1hr and 2hrs.

Based on NICE Guidelines (1hr postprandial levels of <7.8mmol/L), she had missed 7 spikes in blood sugar levels over 2 weeks, yet by the 2hr mark, her levels were below the recommended guideline of <6.4mmol/L on all those occasions. Imagine how many spikes could have been missed throughout the remainder of her pregnancy if she had continued testing only at the 2hr mark!

a comparison of 1hr and 2hr blood glucose testing

Any testing is better than no testing

We should point out that any blood glucose monitoring is better than no monitoring at all. Capillary blood glucose monitoring is just a guideline, but it will help build up a good picture as to what is happening in your body and can help you understand the impact different foods and drinks are having on you.

That said when you test and the targets used can also make a huge impact on how your gestational diabetes is managed and controlled.

The more you test, the more you can see and build a much bigger picture. You can learn which foods you struggle with and tweak meals accordingly. Taking this approach can mean that you stay diet controlled for longer, or lower amounts of medication or insulin are required

If you believe testing more often or at different times than what your diabetes team have recommended could be beneficial to managing your gestational diabetes, then discuss this with your team and explain the reasons why along with the guidelines and research that suggest when the best times for testing are

Spike Testing

What is spike testing?

Spike testing is testing blood sugar levels much more frequently after consuming foods/drinks to see the impact on blood sugar levels with the aim to tweak diet accordingly to allow better control of blood sugar levels.

How did spike testing originate?

Spike testing developed after seeing some ladies in our Facebook group getting away with eating some extremely high processed carb meals washed down with full sugar fizzy drinks or pure fruit juices etc.

We saw in the Facebook group that often ladies would admit or confess to eating some very questionable things (a large slice of chocolate fudge cake, Krispy Kreme doughnuts, Chinese sweet and sour chicken with rice & chips e.t.c.) and then get absolutely amazingly low levels afterwards, therefore presuming that they tolerated this suspiciously high carb treats/meals really well.

Many times, they would also not admit to their professionals that they were eating these things and ‘getting away with it’, yet were coming into the group asking why it was they could tolerate these things – the question was, were they really?

Once seeing that good levels are achievable with these things, they continue to eat them – why wouldn’t they if the blood sugar levels look fine?

We regularly saw posts such as these in our Facebook group: “I can’t touch a piece of bread, yet I’m fine with Krispy Kreme doughnuts?!”, “I get better levels eating rubbish than I do eating healthy. It makes no sense?”

missing the spike
Good tolerance or has this Mum missed the spike?

Unfortunately, some would then post that their baby has jumped up to the highest centiles in the high 90s > 100s and beyond despite great levels and/or the baby was born puffy, swollen and poorly with complications linked to GD.

Thinking outside the box

We knew that to treat a hypo, you can have glucose and see the response in blood sugar levels at 15 minutes and saw from research​6–15​ that continual or flash blood glucose monitoring can be extremely beneficial in diabetic pregnancies, being able to see the impact all foods/drinks were having on blood sugars and being able to adjust their diet and insulin doses accordingly.

Also in the knowledge that different types of foods and even different types of carbs release at different rates and in different amounts in the bloodstream, it was at that point that it was suggested that it may be worthwhile checking what the body was doing after having these high glucose hits from high carb choices.

This is where some mothers decided to start testing certain things before the 1-hour or 2-hour test time, or after foods when they normally test only pre-meals as advised by their hospital.

The initial advice was to test at 15mins (knowing that treating a hypo, you would expect to see a spike after this time), 30 mins, 1hr, 90mins and 2hrs. Hopefully, this would be enough to catch all major spikes in levels and you would see a gradual rise and fall in levels, therefore ensuring that the glucose has been processed effectively. By testing at these times they would be able to see how high levels are spiking and to see if having an excessive glucose load is causing some of these ladies to have a spike and crash, something that is also seen in diabetics where controlling blood sugar levels is a problem.

What we saw was that indeed, some of these ladies were getting some extremely high levels and then crashing low at their actual test time, which then meant their bodies went on a rollercoaster of dumping more glucose to pull blood sugar levels back up and then spiking again. It was a vicious cycle of spiking and crashing like a rollercoaster.

blood sugar rollercoaster

Finding this information out meant that these ladies were able to see that actually they may not have been ‘tolerating’ these types of foods as well as they first thought and gave them the chance to try alternatives that would keep blood sugar levels more stabilised (like rolling hills, rather than rollercoasters!)

Over the years this has developed amongst members and many ladies have changed spike testing to ‘test every 15 minutes’. It is not what was originally recommended, however without having a continuous or flash glucose monitoring system (like the Freestyle Libre) fitted, some mothers have felt more in control of their GD by doing this.

The recommendation has always been to reserve spike testing for treat-type foods which you think may push the boundaries, not to test all carbs or all foods in this way

But doesn’t everyone’s blood sugar levels spike?

Yes, they do. Blood sugar levels spike in all people (diabetic and non-diabetic). The spike in blood sugar levels after eating is what signals the pancreas to release insulin and process the sugar.

However, what we are looking at with spike testing is how high the spike is reaching, for how long and then how well our body is processing that sugar. With an ultimate goal of achieving good, stabilised blood sugar levels.

What are the targets for spike testing?

There are no targets for how high blood sugar levels should be before one hour and so some mothers feel they do not want their levels to go beyond their upper test limit at any time (as a way to play safe). In my opinion, this is too extreme.

Spike testing can be extremely beneficial to those that want to push their dietary boundaries slightly, to check how well they are tolerating higher carb/sugar loads and as long as there is a gentle rise and fall in levels, it shows that the body has processed these sugars well.

Whereas some spiking into high double figures within the hour and crashing down to very low levels feel it is a concern and shows that the body has not coped at processing this glucose as well as a non-diabetic would. The concern is that whilst levels were so extremely high (knowing that it is present in the blood) that this would not be good for the baby trying to regulate their own insulin response.

Why does my hospital not tell me to spike test?

The majority of hospitals do not advocate spike testing, although some consultants and teams agree that it can be beneficial to managing GD if the mother is happy to do it.

Spike testing is an inconvenience to the patient and it is costly for the NHS to provide the consumables.

Many professionals feel that as long as blood sugar levels are within target at the recommended test time then there is no cause for concern as the body has processed the sugar sufficiently and they feel the 1-hour or 2-hour level is the most important figure to look at.

Does spike testing cause more damage than it’s worth?

Some people feel that spike testing can cause additional stress and anxiety at a time when the mother is already vulnerable after being diagnosed with gestational diabetes. Women with gestational diabetes already have an elevated risk of developing postpartum depression symptoms​16​ and so anything that causes additional stress or anxiety is obviously not good for the mother or baby (or blood sugar levels as stress can cause higher levels!)

It can also cause some mothers to become obsessive over blood sugar levels, which may also cause negative impacts such as anxiety.

There is also the physical discomfort of testing multiple times and so this is why this method should not be used for all meals/food eaten.

NO ONE HAS TO SPIKE TEST, it’s just something some mothers like to do in the absence of a CGM system. If you feel it would cause more stress or anxiety then it is not advisable to do it

Research on spike testing

There are no research studies on ‘spike testing’ by capillary testing with a home blood glucose monitor. Spike testing is something that has been created from within our Facebook support group between mothers as a way of gaining better control of their GD. When talking about any evidence of spike testing being beneficial, the evidence has been compared to the research on continual glucose monitoring in pregnancy (please see links at the bottom of the page).

CGM is not available to mothers with GD (apart from in exceptional circumstances, during research trials, or at a cost to the mother) and so this is the closest way GD mothers have been able to achieve the same level of knowledge and control.

Do I need to spike test GD UK cake and sweet treat recipes?

No. All GD UK recipes are made with ingredients that should not cause high spikes in blood sugar levels. The recipes are self-paired, meaning they are a balance of better carbs, high in fat and protein, which helps slow down the release of glucose into the bloodstream, therefore designed to keep levels more stabilised.

Advice around stopping testing or reducing testing

Some mothers are advised to reduce testing or completely stop following good blood sugar level results.

Bearing in mind that these mothers have tested positive for gestational diabetes, did have higher levels when not following a good GD diet and in the knowledge that gestational diabetes is a progressive condition that worsens as the pregnancy goes on, then you may want to carry on testing to see how your levels are.

Typically, gestational diabetes worsens from 32-36 weeks and so if you have been advised to reduce or stop testing at this time, you may want to continue for peace of mind.

Having great control of blood sugar levels towards the end of pregnancy and through labour can really help the baby regulate their own insulin production, which in turn means they are more likely to have stable blood sugar levels after birth and avoid the complication of neonatal hypoglycaemia.

thumbs up
you decide and carry on testing if you want

It’s your pregnancy, it’s your baby. Use your B.R.A.I.N and make an informed decision over test times and targets to use

BRAIN informed consent


  1. 1.
    Ecker L, Greene M. Hyperglycemia and Adverse Pregnancy Outcomes. NEJM. Published online May 8, 2008. doi:10.1056/NEJMoa0707943
  2. 2.
    SIGN Guidelines 116 – Management of Diabetes. SIGN – Healthcare Improvement Scotland; 2017:59. Accessed May 30, 2019.
  3. 3.
    1.3 Antenatal care for women with diabetes. NG3 Diabetes in pregnancy: management from preconception to the postnatal period. Published February 25, 2015. Accessed May 30, 2019.
  4. 4.
    5.3.6 Blood Glucose Targets during Pregnancy. HSE; 2010:52. Accessed May 30, 2019.
  5. 5.
    5.1 Monitoring Blood Glucose and Ketones during Pregnancy 5.1.1 Blood Glucose Monitoring. NICE; 2015:328-348. Accessed May 30, 2019.
  6. 6.
    Yogev Y. Continuous glucose monitoring for treatment adjustment in diabetic pregnancies—a pilot study. Diabetic Medicine. 2003;20(7):558-562.
  7. 7.
    Bühling KJ. Introductory Experience with the Continuous Glucose Monitoring System (CGMS®; Medtronic Minimed®) in Detecting Hyperglycemia by Comparing the Self-Monitoring of Blood Glucose (SMBG) in Non-Pregnant Women and in Pregnant Women with Impaired Glucose Tolerance and Gestational Diabetes. Experimental and Clinical Endocrinology & Diabetes. 2004;112(10):556-560.
  8. 8.
  9. 9.
    Kirsimarja KK. Continuous glucose monitoring versus self-monitoring of blood glucose in the treatment of gestational diabetes mellitus. Diabetes Research and Clinical Practice. 2007;77(2):174-179.
  10. 10.
    McLachlan K. The role of continuous glucose monitoring in clinical decision‐making in diabetes in pregnancy. Australian and New Zealand Journal of Obstetrics and Gynaecology. 2007;47(3):186-190.
  11. 11.
    Chen R. Continuous glucose monitoring for the evaluation and improved control of gestational diabetes mellitus. The Journal of Maternal-Fetal & Neonatal Medicine . 2009;14(4):256-260.
  12. 12.
    Sung JF. Continuous Glucose Monitoring in Pregnancy: New Frontiers in Clinical Applications and Research. Journal of Diabetes Science and Technology. 2012;6(6):1478-1485.
  13. 13.
    Mazze R. Measuring glucose exposure and variability using continuous glucose monitoring in normal and abnormal glucose metabolism in pregnancy. The Journal of Maternal-Fetal & Neonatal Medicine. 2012;25:1171-1175.
  14. 14.
    Fan Yu. Continuous Glucose Monitoring Effects on Maternal Glycemic Control and Pregnancy Outcomes in Patients With Gestational Diabetes Mellitus: A Prospective Cohort Study. The Journal of Clinical Endocrinology & Metabolism. 2014;99(12):4674–4682.
  15. 15.
    Lane A. 85: Real-time continuous glucose monitoring in gestational diabetic pregnancies: a randomized controlled trial. AJOG. 2019;220(1):S68–S69.
  16. 16.
    Azami M. The association between gestational diabetes and postpartum depression: A systematic review and meta-analysis. Diabetes Research and Clinical Practice. 2019;149:147–155.