Gestational diabetes: Does a routine examination help to avoid complications for mother and child?

A routine examination can help to identify women who have possibly developed gestational diabetes. Treating gestational diabetes could help lower the risk of some complications during birth.

Women with gestational diabetes (diabetes during pregnancy) have temporarily high blood sugar levels. This is usually not a cause of concern, and often does not lead to any problems. But some women will have an increased risk of particular complications during pregnancy and birth. These can affect both the mother as well as the child.

It is not always easy to say where having slightly elevated blood sugar levels ends and gestational diabetes begins. It is normal that a woman’s metabolism changes over the course of pregnancy. During this time the body generally absorbs sugar from the bloodstream more slowly after a meal. This means that high blood sugar levels are not unusual in many pregnant women – and they usually return to normal levels once again after pregnancy.

Having gestational diabetes does not mean that you have developed diabetes mellitus. Diabetes mellitus is a long-term chronic disease, while gestational diabetes usually goes away after birth. But women with gestational diabetes are somewhat more likely to develop diabetes mellitus type 2 later in life. In rare cases diabetes that had apparently already developed before is discovered during the pregnancy. You can learn more about diabetes here (URL: http://www.gesundheitsinformation.de/index.518.56.en.html) .

On the other hand, when blood sugar levels rise, the risk of certain problems during pregnancy or childbirth is higher. Women who develop gestational diabetes are more likely to have larger babies (weighing more than 4,000 grams at birth). This makes it more likely for there to be difficulties when the baby passes through the birth canal, which can delay the birthing process. Yet these mostly involve complications that almost always have no lasting repercussions for mother or child. What is more, in 2008 almost every tenth baby born in Germany weighed over 4,000 g at birth, without any problems occurring during birth for the overwhelming majority. Mother and child were completely healthy.

What is more, high levels of blood sugar increase the risk of a pregnant woman developing a rare disorder associated with high blood pressure – what is called preeclampsia. In preeclampsia, the pregnant woman’s blood pressure is very high, and proteins released through the kidneys can be found in the urine. Without treatment this disorder can result in harm for both mother and child.

A diagnosis of gestational diabetes means taking certain precautions: the pregnancy is then considered a high-risk pregnancy – this is in itself unsettling news. What is more, the woman is advised to re-examine her lifestyle in order to lower the high levels of blood sugar by possibly making changes in her behavior. This involves healthy eating, getting enough exercise and regularly checking blood sugar levels. If needed, injecting insulin for the duration of the pregnancy is also recommended.

Diagnosis of gestational diabetes

To diagnose gestational diabetes, women take a so-called oral glucose tolerance test (OGTT). This measures how the metabolism reacts to sudden intake of large amounts of sugar. The pregnant woman must drink a concentrated sugar solution in the morning on an empty stomach (this means that she should fast for at least 8 hours before taking the test) – some blood is drawn and blood sugar is measured, both beforehand and afterwards. There is also a shorter version of the test that involves drinking a smaller amount of sugar solution and then only having blood drawn once after one hour; this test cannot be done on an empty stomach. According to current knowledge, this test does not involve any risk to the baby. But some women find it unpleasant – especially having to drink the extremely sweet liquid. You can read about how the glucose tolerance test is done exactly here (URL: http://www.informedhealthonline.org/index.733.en.html) .

Medical associations and other institutions have been calling for the introduction of a routine examination for gestational diabetes for years. This type of testing, where all members of a certain group – in this case all pregnant women – are offered a test, is also called screening. Screenings are usually associated with the hope of being able to detect and treat diseases early, but they also have advantages and disadvantages. There is a risk of classifying someone as sick due to inexact tests, although they are in fact healthy (this type of result is called a false positive).

So in the case of gestational diabetes, one question is: Should this type of test be offered to all women or only to women who have certain risk factors? For example, heavily overweight women as well as women who have already had gestational diabetes run a higher risk of gestational diabetes. A pregnant woman’s relatives having had diabetes mellitus also increases the likelihood that she develops it herself.

Little research on routine examinations for gestational diabetes

Together with researchers at the Medical University of Graz, the Institute for Quality and Efficiency in Health Care (IQWiG) – the publisher of this website – examined what benefit there is in routinely offering all pregnant women a test for gestational diabetes. The researchers looked at

• whether this type of screening influences the frequency of complications from gestational diabetes,
• whether expectant mothers and / or their children profit from the treatment of gestational diabetes,
• which testing procedure is the best and,
• whether screening for gestational diabetes has any adverse effects.

Although this routine examination has been recommended for years, its advantages and disadvantages have not been studied in any reliable trial. For this reason the researchers were not able to answer the first and most important question of all by drawing on trials that would have been ideally suited: namely, whether screening all pregnant women for gestational diabetes helps to avoid complications for both mother and child. They did not find any studies comparing whether complications more frequently arose in women who were not screened than in women who were offered screening for gestational diabetes.

Treatment can have positive effects

The second question that researchers examined: Is there a treatment for gestational diabetes that profits expectant mothers and/or their children? Because routine examination for gestational diabetes only makes sense if there is also an effective treatment for it. The IQWiG researchers analyzed 25 trials testing whether treating gestational diabetes helps to prevent complications. In some trials the women who had gestational diabetes were identified by using certain screening strategies.

The research shows that treating gestational diabetes lowers the number of babies with a high birthweight (over 4,000 g): This number was lowered by a little more than half – from an average of 16 out of every 100 to 7 out of every 100 babies. But the researchers from IQWiG did not consider a birthweight of over 4,000 g alone to be a cause of concern for the health of the child.

The researchers also found 2 trials that tested whether the risk of having a certain complication of childbirth sank, so-called shoulder dystocia. In shoulder dystocia the baby’s shoulders are delayed from coming out after the head has already come out. Shoulder dystocia is more common when giving birth to larger babies. Sometimes the child is stuck temporarily, but rarely this can last for a longer time. If this happens, the infant is at risk of not getting enough oxygen. Because as a precaution obstetricians and midwives take quick action to stop this from happening, the child can often be slightly injured. The mother is also at risk of injury, but this is less common. Emergency and serious injuries rarely result. Even though these injuries almost always heal without lasting bodily harm, the situation can be traumatic for the mother and affect them emotionally.

In both trials it was possible to lower by more than half the number of shoulder dystocias by treating gestational diabetes: While there was a delay in the birthing process in 3.5 % of the births without treatment, after treatment this was the case in only 1.4 % of the births.

One trial suggested that a woman who has gestational diabetes is less likely to develop preeclampsia with high blood pressure (see above) if she is treated for gestational diabetes.

Disadvantages or harm resulting from treating gestational diabetes were not explicitly studied in the trials, so they were not reported, either. None of the trials provided information about whether the treatment of gestational diabetes has long-term health benefits for the mother and/or child.

Possible disadvantages of routine examination

Even if there is a helpful treatment, this does not automatically mean that routine examination for all pregnant women is also a good idea. Most of them do not need such a test anyway, because they have normal blood sugar levels. And many women who have gestational diabetes would already be diagnosed anyway as part of their usual pregnancy check-ups, especially women who are at high risk. What is more, routine examinations can have possible harms as well as benefits.

In the case of screening for gestational diabetes, neither the benefits nor the harms have been studied enough. In light of this uncertainty the IQWiG has put together a list of possible disadvantages of screening and assessed their importance. Examples of possible disadvantages are:

• The effort of doing the test as well as its adverse effects: It may be that a woman becomes nauseous or has to vomit as a result of having to drink the sugar solution.
• Women without gestational diabetes are possibly mistakenly categorized as having a high-risk pregnancy by an inexact test and then treated for no reason (false positive test results). Unnecessary treatments have adverse effects, but no benefit.
• The diagnosis “gestational diabetes” could unsettle the women who receive it.
• Treating gestational diabetes can have adverse effects, for example hypoglycemia (having a lower than normal level of blood sugar) as a result of a strict diet and/or an insulin dose that is too high.
• The treatment of gestational diabetes does not have a benefit for all women, because pregnancy and childbirth would have gone smoothly without being treated.

Under the condition that pregnant women have been well informed, the researchers considered the possible disadvantages of screening as not being so severe that they outweigh possible benefits. The IQWiG supposes that by screening for gestational diabetes childbirth complications can be somewhat reduced.

Different options for doing a routine examination

The IQWiG’s conclusion applies only under the condition that the screening is carried out as it is described in the trials that were analyzed. In the trials that show that the therapy has a benefit, the women were all selected and diagnosed according to a very specific strategy. As a first step, all participants took a one-hour glucose test that they did not need to fast for. Then, only the women who had high blood sugar levels (about 25% – that is, about 25 out of every 100 women) took a longer test a few days later. For this test the women had to come to the doctor’s office on an empty stomach and their blood sugar was checked over the course of 2 to 3 hours. Most of the women whose blood sugar levels were high in the first test were not found to have gestational diabetes. In the end – as the second test showed – only about 3 to 4% of all the women who were examined had above-average levels (about 3 to 4 out of every 100 women). Their gestational diabetes was diagnosed and then treated.

The IQWiG finds this two-step approach to be the best-studied. Other tests for gestational diabetes, which for example only take a one-step approach, have not been studied enough. They can lead to women being diagnosed as having gestational diabetes without it being clear whether they can really profit from treatment. Another option, therefore, is to offer a glucose tolerance test only to women who have certain risk factors such as older age, being overweight or diabetes in the family. It might also happen that treatment for a woman is recommended that is too strict, although she has only slightly elevated blood sugar levels. Therefore, the IQWiG finds that a trial is badly needed that directly compares the advantages and disadvantages of the different screening strategies for expectant mothers and their children.

Author: German Institute for Quality and Efficiency in Health Care (IQWiG)

Note

This health information is a summary of a scientific report published by IQWiG. It is not an assessment of the right to have health care services reimbursed by statutory health insurance funds in Germany. By law, decisions about the reimbursement of diagnostic and therapeutic procedures can only be made by the German Federal Joint Committee (G-BA). The Federal Joint Committee takes IQWiG reports into consideration in its decision-making process. You can find information about the decisions of the German Federal Joint Committee on its English-language website www.english.g-ba.de (URL: http://www.english.g-ba.de) .

Next planned update: March, 2014. You can find out more about how our health information is updated here (URL: http://www.gesundheitsinformation.de/our-methods.643.en.html?bab[subpage_id]=0-8) .