How are blood sugar levels measured?

Gestational diabetes usually doesn’t cause any noticeable symptoms. The best way to find out whether there is too much sugar in your blood is by doing a glucose tolerance test. This test measures how well the body can process larger amounts of sugar. If the blood sugar measured in the test is above a certain level, it could be a sign that sugar isn’t being absorbed enough by the body’s cells. Gestational diabetes or “normal” diabetes might be the cause.

The glucose tolerance test is offered in pregnancy between the start of week 24 and the end of week 27. A similar, simpler test is done first:

• Glucose challenge test: This first test is done to find out whether it makes sense to do the actual, more involved diagnostic test. If the results of this test show that a woman's blood sugar levels are elevated, it doesn’t necessarily mean that she has diabetes.
• Glucose tolerance test: This test is done if the results of the challenge test are abnormal. It can determine whether you have gestational diabetes. It is also called the "oral glucose tolerance test."

You can decide whether you want to do this screening test or not.

What does it involve?

In the challenge test, you drink a glass of water with 50 grams of sugar dissolved in it. One hour later, blood is taken from a vein in your arm to measure your blood sugar levels. If the value is below 7.5 millimoles per liter (mmol/l, which is about 135 mg/dl), the results are considered to be normal and no more tests are done.

Unlike the challenge test, the glucose tolerance test has to be done on an empty stomach. In other words, you shouldn’t eat anything for at least eight hours beforehand. You're only allowed to drink still mineral water or tap water during this time. At the beginning of the test, a blood sample is taken. You then drink a sugar solution containing 75 grams of glucose dissolved in 300 ml of water. A blood sample is taken from a vein in the arm one hour later, and then again after two hours. If any of the following three blood sugar levels is reached or exceeded, gestational diabetes is diagnosed:

• After fasting: 5.1 mmol/l (92 mg/dl)
• After one hour: 10.0 mmol/l (180 mg/dl)
• After two hours: 8.5 mmol/l (153 mg/dl)

The test results are documented in your maternity records. In Germany, the costs of glucose tolerance tests are covered by statutory health insurers.

There are no known risks to the unborn child. Some women find the sugar solution unpleasantly sweet.

What are the benefits of this routine test?

The benefits of this routine screening test haven’t yet been looked at in comparative studies. So it isn’t exactly clear what advantages and disadvantages it may have. If the diagnosis made it possible to treat the diabetes early enough, and that was shown to lower the risk of complications at birth, for instance, then that would be an advantage.

The research so far has shown the following:

• Treating gestational diabetes reduces the likelihood that the child will weigh more than 4,000 grams at birth.
• Treatment reduces the risk of one of the child’s shoulders getting stuck in the mother’s pelvis during the birth (shoulder dystocia), which also reduces the risk of injury to the mother and child.
• Many women who are diagnosed with gestational diabetes don’t have any related problems during pregnancy or childbirth.

Although the pros and cons of the test haven’t been thoroughly researched, it is thought that the advantages outweigh the disadvantages and that screening for gestational diabetes can somewhat lower the risk of complications in childbirth.

What are the possible disadvantages of a routine screening test?

All screening tests and examinations have disadvantages as well as advantages. Even if there is a treatment that works, it doesn’t necessarily mean that a routine examination for all pregnant women is a good idea. Routine tests for gestational diabetes are unnecessary in most pregnant women because their blood sugar levels are normal. And doctors might recognize that a woman is at greater risk of developing gestational diabetes anyway, while providing the standard care during pregnancy.

Being diagnosed with gestational diabetes can make women worry for no reason. Higher-than-normal blood sugar levels don’t necessarily cause problems. Most pregnant women with slightly higher blood sugar levels give birth to healthy babies with a normal birth weight. After receiving the diagnosis, women are also advised to change their diet and measure their blood sugar several times a day. There isn't always a real need to do this, though.

How do women feel about the diagnosis?

Many women are very surprised by the diagnosis because they never thought of the possibility. Others blame themselves and think that they must have done something wrong. Many are worried at first because they don't know what the diagnosis means for their baby and the rest of their pregnancy, and what steps need to be taken. So it's important to find out more about the condition. Simple, easy-to-follow advice about how to treat gestational diabetes can be particularly helpful here.

Many women would like to have emotional support in coping with gestational diabetes – both from their doctors and their family. Some also see the diagnosis as an opportunity to change their lifestyle.

Sources

• Craig L, Sims R, Glasziou P, Thomas R. Women's experiences of a diagnosis of gestational diabetes mellitus: a systematic review. BMC Pregnancy Childbirth 2020; 20(1): 76. [PMC free article: PMC7006162] [PubMed: 32028931]
• Farrar D, Simmonds M, Bryant M et al. Treatments for gestational diabetes: a systematic review and meta-analysis. BMJ Open 2017; 7(6): e015557. [PMC free article: PMC5734427] [PubMed: 28647726]
• Figueroa Gray M, Hsu C, Kiel L, Dublin S. "It's a Very Big Burden on Me": Women's Experiences Using Insulin for Gestational Diabetes. Matern Child Health J 2017; 21(8): 1678-1685. [PubMed: 28092062]
• Gemeinsamer Bundesausschuss (G-BA). Richtlinien über die ärztliche Betreuung während der Schwangerschaft und nach der Entbindung („Mutterschafts-Richtlinien“). 2023.
• Institute for Quality and Efficiency in Health Care (IQWiG, Germany). Search update for report S07-01 - Screening for gestational diabetes; working paper; Commission GA09-02. 2010.
• Institute for Quality and Efficiency in Health Care (IQWiG, Germany). Screening for gestational diabetes: Final report; commission S07-01; Version 1.1. 2009. [PubMed: 23101079]
• Skar JB, Garnweidner-Holme LM, Lukasse M, Terragni L. Women's experiences with using a smartphone app (the Pregnant+ app) to manage gestational diabetes mellitus in a randomised controlled trial. Midwifery 2018; 58: 102-108. [PubMed: 29329023]
• Tieu J, Shepherd E, Middleton P, Crowther CA. Dietary advice interventions in pregnancy for preventing gestational diabetes mellitus. Cochrane Database Syst Rev 2017; (1): CD006674. [PMC free article: PMC6464792] [PubMed: 28046205]

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