Nutritional counselling in pregnancy to prevent gestational diabetes

This fact box will help you to weigh the benefits and harms of nutritional counselling in pregnancy to prevent gestational diabetes. The information and numbers are based on the best scientific evidence currently available.

This fact box was developed by the Harding Center for Risk Literacy.

What is gestational diabetes?

Changes in a woman’s metabolism during pregnancy can temporarily lead to higher blood sugar levels. Gestational diabetes is a condition in which the blood sugar level reaches or exceeds the threshold levels several times. Approximately 4 out of 100 women develop gestational diabetes [1].

In most cases, the blood sugar levels return to their former levels after giving birth. Gestational diabetes therefore does not necessarily permanently lead to the metabolic disorder diabetes mellitus [1].

Risk factors for increased blood sugar levels are:

  • overweight (Body Mass Index (BMI) > 25),
  • obesity (BMI > 30) before pregnancy,
  • and gestational diabetes in the past.

Additionally, pregnant women may have higher blood sugar levels if close relatives suffer from diabetes [1].

One of the possible consequences of gestational diabetes is that newborns are on average bigger and heavier at birth (over 4,000 or 4,500 g) [1]. This increases the risk of injuries during birth to the mother or the child (e.g., injuries to the genital area of the mother or the child’s shoulders getting stuck in the mother’s pelvis). Furthermore, the birth may be slowed down, which increases the risk of complications (e.g., reduced oxygen supply to the child) and of a caesarean section [2]. However, such emergency situations are rare [1].

High blood sugar increases the likelihood of the rare pregnancy disorder pre-eclampsia, which is characterised by increased blood pressure and a higher protein content in the urine. It can lead to waterfluid retention (edema). An untreated pre-eclampsia can be harmful to mother and child [1].

How is gestational diabetes diagnosed?

If certain risk factors are present, women can be tested for gestational diabetes in the 24th or 28th week of pregnancy (the sixth or seventh month). The test is a standard examination that is covered by statutory health insurance. Its aim is to determine the body’s reaction to a high sugar intake [3].

How does the test work?

During the glucose tolerance test the first step is to drink 50 g of sugar (glucose) dissolved in 250 to 300 ml of water. After one hour the blood sugar level is measured. If the sugar content exceeds the normal level of 7.5 millimoles per litre (mmol/L, 135 mg/dL), an additional test is done. First, a blood sample is taken on an empty stomach. That means not eating or drinking anything (except for water) at least eight hours before the test. After the blood sample is taken, the next step is to drink 75 g of sugar dissolved in 250 to 300 ml of water. An hour later, and then two hours later, another two blood samples are taken. Gestational diabetes is present when one or more of the blood sugar values reach or exceed the following threshold levels:

  • after fasting value: 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) [1].

What is nutritional counselling?

A varied diet before and during pregnancy is assumed to reduce the risk of having high blood sugar levels. Therefore, the objective of nutritional counselling is to increase women’s awareness of their diet and to reduce potential risk factors for the development of gestational diabetes. However, due to metabolic changes during pregnancy, gestational diabetes can happen to any pregnant woman [1].

Fact box_gestational diabetes_EN

What does the fact box show?

The fact box compares the benefits and harms of nutritional counselling and standard care in preventing gestational diabetes. Pregnant women either received nutrition counselling or did not before their blood sugar level was tested (glucose tolerance test).

The table may be read as follows:

About 13 out of every 100 pregnant women with or without nutritional counselling developed gestational diabetes.

About 10 out of every 100 women without nutritional counselling and about 3 out of every 100 women with nutritional counselling developed high blood pressure due to pregnancy. This means, that in about 7 out of every 100 women nutritional counselling could prevent high blood pressure due to pregnancy.

The numbers in the fact box are rounded. They are based on 11 studies with about 2,800 participants [1].

What other aspects should be considered?

The women who participated in the study did not have type I or type II diabetes prior to their pregnancy. Nor had they had ever been tested for gestational diabetes before or taken part in other measures to prevent excessive weight gain.

The studies do not indicate whether the women were already overweight or obese before pregnancy.

Furthermore, the studies are very diverse, varying in their research topics, the points of time at which they were carried out, and their testing frequency.

Do the results provide proof (evidence) for the benefits and harms of nutrition counselling?

Overall, the evidence is of low to very low quality:

It is very likely that the results regarding high blood pressure, pre-eclampsia, and the necessity of a caesarean section will change with further research (low quality of evidence).

The results regarding the incidence of gestational diabetes and injuries to the genital area are not trustworthy (very low quality of evidence).

Last update

January 2018

Icon Array visualizing the data

Icon Array Gestational Diabetes
© Harding Center for Risk Literacy


Information within the fact box was obtained from the following sources:

[1] Institut für Qualität und Wirtschaftlichkeit im Gesundheitswesen (IQWiG). Schwangerschafts-diabetes 2017 [Available from: www.gesundheitsinformation.de/schwangerschaftsdiabetes.2108.de.html.

[2] Tieu J, Shepherd E, Middleton P, et al. Dietary advice interventions in pregnancy for preventing gestational diabetes mellitus. Cochrane Database Syst Rev2017(1):CD006674.

[3] Gemeinsamer Bundesausschuss. Früherkennungsuntersuchungen im Überblick 2016 [Available from: www.g-ba.de/institution/themenschwerpunkte/frueherkennung/ueberblick/ accessed 16.01.2018

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