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Disorders of blood glucose levels in pregnancy are relatively common. In a representative Australian population about 1-2% of women with pre-existing diabetes become pregnant. This type of diabetes is usually insulin treated type 1 diabetes or type 2 diabetes with various treatments ranging from diet alone, oral hypoglycaemic agents (tablet(s)) to insulin.

However, relatively minor elevations of glucose levels during pregnancy, a condition called gestational diabetes mellitus (GDM) are associated with a range of adverse maternal and fetal outcomes. The most common problems are a large for gestational age baby leading to birthing problems, an increased rate of caesarean section and an increased rate of admissions to a special care nursery. Evidence is now accumulating that problems in childhood may be related to the effects of intrauterine programming linked to high glucose levels in the mother. It is not only the “average” maternal glucose level that is associated but also the fluctuations (usually highs) that can happen in the mother, invariably related to diet.

It is recommended that all women are tested for diabetes in every pregnancy. Conventionally this is around 28 weeks gestation, but early testing is recommended for women with risk factors – a family history of diabetes, previous GDM, high risk ethnic groups, etc…

In Australia, the majority of women diagnosed with GDM are referred to a specialist Diabetes Centre and a see a diabetes educator and a dietitian. The diabetes educator will usually arrange for access to a lancing device (finger pricker) and home blood glucose meter and give instruction on its use. Women are all asked to measure their fasting glucose level, either one or two hours after each of the three major meals. There are strict criteria about the upper range of the glucose levels. If either the fasting level or the after-meal level (post prandial) are exceeded, then it is usual to advise the use of insulin injections. Clearly this is a situation and recommendation that most women would like to avoid.

Pregnant woman

The dietitian has two major roles. The first is to ensure that the overall diet for the pregnancy is suitable and nutritionally sound for both the mother and the developing fetus. The second is to ensure that the glucose targets fasting and after meals are not exceeded. It is here that knowledge and application of a low GI diet is critical.

The dietitian will ensure that the diet contains an adequate amount of low GI carbohydrates and that this is distributed as evenly as possible throughout the day. A common example is to advise women to have two carbohydrate exchanges (15 g each) at the three major meals and to have one exchange with snacks. A 15 g exchange might include a slice of bread, or an apple, or a medium potato. For some women this might involve a redistribution of their daily food intake, especially with the evening meal.

With strict attention to the diet, most women will avoid the need to use insulin to help lower their glucose levels. The low GI diet choices really work. In a major clinical trial, women with GDM were randomised to either a low GI diet or a conventional diet in pregnancy and observed.

Women on a conventional diet were far more likely to meet the criteria to commence on insulin. However, if they were then changed to a low GI diet, about half could avoid having to use insulin.

Low GI dietary advice is not just suitable for women with GDM. While women with GDM are an obvious choice for intervention, normal pregnant women with glucoses in the higher range have more adverse pregnancy outcomes than women in the lower range – hence a low GI diet is suitable and advantageous for all women in every pregnancy.

A low GI diet makes common sense for everybody. It is especially relevant in pregnancy where it has been shown to improve pregnancy outcomes.

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Bob Moses  
PROFESSOR ROBERT MOSES, OAM is an international authority on diabetes and its treatment. Since opening an endocrinology practice in Wollongong in 1975, his interest and referral base has developed to focus on diabetes and problems that can arise during pregnancy, particularly gestational diabetes.
Contact: Illawarra Health and Medical Research Institute