Is Routine Testing For Gestational Diabetes Necessary?

Is Routine Testing For Gestational Diabetes Necessary?

High blood sugar during pregnancy, known as gestational diabetes mellitus (GDM), used to be a rare condition, occurring in about 3% of pregnancies.

In recent years, the rate has doubled – up to 8% of pregnant women are diagnosed with GDM.

With new recommendations lowering the cutoff point for diagnosis, a dramatic increase in GDM rates is expected; experts predict it could be up to 15%.

Not all medical professionals agree with routine testing to diagnose GDM, however, and question whether GDM is a pathological problem in such high numbers, or simply part of pregnancy.

Is Routine Testing For Gestational Diabetes Necessary?

Dr. Sarah Buckley, author of Gentle Birth, Gentle Mothering recommends most women avoid the routine test.

Dr. Michel Odent, world-renowned obstetrician and birth specialist, and Henci Goer, expert on evidence-based maternity care, both believe diagnosis of GDM increases risk and stress unnecessarily.

Most pregnant women will have to decide whether or not to take the gestational diabetes screening test.

Women who are offered the test might not know anything about GDM, the risk factors, the accuracy of the screening tests, or what failing the test could mean.

For many women, negotiating their way through GDM screening is a challenge, especially for those who decide to forgo having the test, or want to know what their options are. Unfortunately, there aren’t many doctors or midwives who support alternative testing for GDM.

What Is Routine GDM Screening?

The test for GDM has traditionally been two-tiered and occurs around 24-28 weeks gestation.

  • Glucose challenge test (GCT): This requires you to drink 50g of sugar solution, one hour prior to having a blood test. You don’t need to fast for this test. If your blood sugar levels are above normal, you will have the second test. Some hospitals are now phasing out the GCT as it has a rate of false negatives/positives.
  • The oral glucose tolerance test (OGTT). This test requires you to fast for 8-12 hours, then have a fasting blood sample collected. You will then be asked to drink 75-100g of sugar, and your blood sugar levels tested 2-3 hours later. If they are above the normal level, you are diagnosed with GDM.

Depending on where you live, you will have the GCT first and, if your levels are elevated, you will be referred on to have the OGTT. However, in some countries, the GCT is no longer used.

The ‘normal’ blood glucose level can vary, depending on where you live.

In the UK, US, Australia and New Zealand, women who have blood glucose levels above 8-9mmol/L (140-160mgdl) two hours after having the OGTT drink are considered above the normal range and are diagnosed with GDM.

Is GDM Testing Accurate?

If you decide to go through with the GDM testing, you want to be confident the results are accurate, right?

A study done in 2012 found the GCT has a sensitivity rate of 76%. This means for every 100 women who have GDM, only 76 will be identified with the GCT. The other 24 women will believe their blood sugar is within the normal range, when in fact they have elevated blood glucose levels.

The researchers also looked at the specificity of the test, which relates to the test’s ability to detect patients without a condition.

The GCT specificity is 76%, meaning for every 100 women without gestational diabetes, 76 will have a negative result, and 24 women who don’t have gestational diabetes will have a positive result!

Based on this research, the GCT should be used only as a screening tool, and not a diagnostic one.

The OGTT test is far more sensitive than the GCT and should be used if a GCT gives a positive result. Because it is more sensitive, the OGTT results in much higher rates of diagnosis.

While this might be a good thing, and ensures women who are risk of having GDM are given the care and support they need, there is a chance more women will face interventions in the birth of their babies.

Another accuracy issue with GDM testing is the results vary depending on what gestation you are.

At week 28 you could fail a test that you could have passed had you taken it a few weeks earlier. This is because pregnancy increases a woman’s insulin resistance over time.

Why Are Women Insulin Resistant During Pregnancy?

In a non-pregnant state, when you eat carbs they are converted to glucose, which circulates in your bloodstream. In response, your body releases insulin to move the glucose from the blood into the cells, where it is used for energy.

When you are pregnant, the placenta produces hormones to help your baby grow, but they also reduce the insulin response, so as to keep more glucose in the blood to be transferred to your baby.

This dampened insulin response is called insulin resistance and it can increase a pregnant woman’s need for insulin by up to 2-3 times more than normal. This drives blood glucose levels up after eating, which gives the developing baby access to more nutrients.

Although this is a normal effect of pregnancy on blood glucose levels, no adjustments are made when blood glucose testing is performed. The glucose solution contains 50g of sugar – the equivalent of about 12 teaspoons.

If your body isn’t used to taking in so much sugar in one go, and is developing insulin resistance normally, thanks to pregnancy hormones, then it will not be able to produce an appropriate amount of insulin in response. It will certainly not have the necessary insulin sensitivity to get that amount of sugar out of the bloodstream.

After having the oral glucose drink, many women report feeling nauseous and unwell, and experience headaches, stomachaches, dizziness and mental fogginess.

These symptoms are especially unpleasant when you’re pregnant, and even more so for those unfortunate women who have severe morning sickness (hyperemesis gravidum) or food aversions.

Who Is At Risk For GDM?

Between 5% and 10% of pregnant women will develop GDM, which usually occurs around the 24th to 28th week of pregnancy.

It isn’t clear why GDM occurs in some women and not others. Several risk factors increase the chances of developing GDM during pregnancy. Women are more at risk if they:

  • Are over 25 years of age
  • Have a family history of type 2 diabetes/GDM
  • Are overweight
  • Are from certain racial groups, such as Asian, Hispanic, American Indian, Indigenous Australian, black
  • Have experienced GD in previous pregnancies
  • Have previously given birth to a macrosomic baby
  • Have had polycystic ovarian syndrome

Women who have at least one or more of these risk factors are advised to be tested for GDM, but more and more birth professionals are calling for routine testing for all women.

On the one hand, this approach makes sense. After all, if we don’t know why GDM occurs in women with no risk factors, wouldn’t it be better to make sure all women are screened?

On the other hand, if insulin resistance is a normally occurring part of pregnancy, then many women could be diagnosed, and receive further treatment/interventions unnecessarily.

What Are The Alternatives?

Many women are questioning the validity of having the GDM testing if they have no, or minimal, risk factors, have a healthy diet and exercise regularly.

However having no risk factors doesn’t automatically mean you can’t develop GDM, especially if you had insulin resistance before becoming pregnant. Many women aren’t aware they are insulin resistant as the symptoms might not present clearly.

Other women are less keen on having the OCTT because of the after effects, and the possibility of being diagnosed with GDM when in fact they don’t have it. While this seems like a small price to pay, their concern is still legitimate.

So, if you aren’t keen on loading your body with a huge amount of sugar, and being diagnosed with a condition you might not have, what can you do?

There are several alternatives, but it’s important to bear in mind there hasn’t been a lot of research done in the area of alternative GDM screening. Your care provider might not support these alternatives, and you should consider your own health and risk factors if you choose not to have the routine testing.

HgA1C Blood Test

The HgA1C test is used to determine your average level of blood sugar over the past 2 to 3 months. It’s typically used to screen for, diagnose, and monitor diabetes and prediabetes, and is around 99% accurate.

If you are in your first or second trimester of pregnancy, this test can determine whether you already had diabetes before pregnancy.

There are no set levels to diagnose GDM with this test, but a high level can be associated with GDM, and will help you to decide whether to have further testing later, after some dietary changes.

Blood Glucose Monitoring

You might choose blood glucose monitoring, which involves checking your blood sugars, at specific times of the day, four times a day, for a week.

You should also keep a food diary to help you be aware of foods that increase your blood sugar levels. Check with your care provider what the acceptable ranges for blood glucose are.

Urine Testing

In some countries, having your urine tested is a routine part of prenatal checks and is done at each appointment.

Glucose urine strips can be purchased for use at home. Be aware, though, one positive test doesn’t necessarily mean you have GDM – especially if you are past the first trimester and have eaten high-sugar foods shortly before testing your urine.

As mentioned above, as your pregnancy progresses, your body resists the efforts of insulin to move glucose from your blood to your cells.

Once you and your baby have used the glucose you need, your kidneys get rid of the excess through your urine. If you had a high-sugar treat before testing, there could be more than normal amounts of glucose to expel, and this could show up on the urine test strip.

The Jellybean Test

If you need to have a GTC or OGTT test done but the thought of ingesting the glucose solution fills you with dread, consider the jellybean test instead.

The OGTT test requires you to consume 50g of sugar in a glucose solution. Depending on the brand and type, you can eat the number of jelly beans that will provide 75g of sugar, and then proceed with the blood test.

This means fewer side effects for those who want to avoid the nasty sugar comedown from the glucose solution. Check labels for sugar amounts in jellybeans, as they can differ between brands.

I Have No Risk Factors And Failed The Test

Today, there is more than enough evidence to show the standard low fat, high refined/processed food diet is less than a healthy option. Obesity rates have been soaring for decades, which  has a knock-on effect of putting women in a high risk category during pregnancy and limiting their birth choices.

Women who are overweight are more likely to develop pregnancy complications that seriously endanger their own health and the wellbeing of their babies. Complications also increase the risks of having interventions or surgical births.

As a result, there has been a resurgent interest in diets based on healthy fats, proteins, and vegetables, with limited intake of processed carbohydrates and sugar.

Often, women who are very healthy, have no risk factors, and habitually limit their intake of refined sugars and carbs are shocked to discover they have ‘failed’ the OGTT test.

They are told they have GDM and need to make adjustments to their diets, possibly have medication or insulin, and might expect a highly interventive birth as a result.

But what if this failed test wasn’t the result of GDM? What if it were simply a case of too much sugar in women whose bodies have adapted to lower glucose intake because they don’t eat the standard western diet?

To answer these questions, neurobiologist and obesity researcher Dr. Stephan Guyenet looked at how the Tukisenta of Papua New Guinea, African Bantu, Native Americans of central Brazil, and iKung African Bushmen handled the OGTT.

The first three groups eat a diet which is very high in carbohydrates (think predominantly grains, starchy vegetables). These three groups were given 100grams of glucose – twice the amount given to women during the OGTT – and then their blood glucose levels were measured after one hour.

All three groups passed the test. Compared with American levels, each group displayed excellent glucose tolerance. Dr. Guyenet concluded that non-industrial cultures that traditionally eat a high carbohydrate diet don’t have high blood glucose levels, because of adaptation; their bodies can move a large amount of glucose out of the bloodstream before levels get too high.

The final group, the iKung African Bushmen, traditionally eat a diet low in carbohydrates compared with Western standards. Researchers gave this group 50grams of glucose and took blood readings one hour later. The levels were extremely high, even compared with American standards. Dr. Guyenet concluded the high OGTT result of the iKung possibly reflects a low habitual carbohydrate intake.

So, if a woman who eats a typically low carbohydrate diet (avoiding high carbohydrate foods such as processed grains and flours), it is likely her body has adapted to using fat as an energy source. If she had an HgA1C test, it would probably show that, over time, her glucose levels were in the low but normal range.

However, if  she were given a large amount of sugar in one dose, it is likely her body simply wouldn’t cope, as it is not used to clearing so much glucose in one go. She would therefore ‘fail’ the OGTT.

You can read more about Why Diet Is A Significant Cause Of Gestational Diabetes and how Diet, Exercise Reduces Gestational Diabetes Risk By Up To 83%.

Recent research has also asked Can Eating Too Much Fruit Cause Gestational Diabetes?

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Sam McCulloch Dip CBEd CONTRIBUTOR

Sam McCulloch enjoyed talking so much about birth she decided to become a birth educator and doula, supporting parents in making informed choices about their birth experience. In her spare time she writes . She is mother to three beautiful little humans.


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