Prof Jennie Brand-Miller answers your questions.
Gestational diabetes. Why such a big deal?
Gestational diabetes (any degree of ‘glucose intolerance’ diagnosed for the first time during pregnancy) is the most common medical problem encountered during pregnancy. The name is derived from the combination of having a raised blood sugar level, as occurs in people with diabetes mellitus, and being pregnant (gestational). While “blood sugar” is the commonly used term, it is actually a measurement of glucose in a blood sample taken from a vein. In practice, the terms are used interchangeably.
A diagnosis of gestational diabetes is important for many reasons. Firstly, it identifies women who may be at risk for developing type 2 diabetes later in life. The forewarning means they can make diet and lifestyle changes, for themselves and their family, to help reduce their chances. Some women, during and after pregnancy, may also be prescribed metformin, a drug that reduces insulin resistance and may prevent or delay the development of type 2 diabetes.
Secondly, women with gestational diabetes are more likely to have a large baby. While normal women without diabetes can also have big babies, the reasons are different and often genetically determined (e.g. both the mother and father are tall). Women with gestational diabetes have bigger babies because high amounts of glucose are converted and stored as fat around the baby’s abdomen. The increased size of the baby’s abdomen can be detected and measured on ultrasound.
A mother with a large baby, whatever the cause, is more likely to have a complicated delivery, with injury to both the baby and the mother. There is an increased rate of medical intervention (e.g. forceps delivery) and higher rate of both elective and emergency caesarean section. In many instances, the detection of a large baby will mean an earlier delivery is scheduled with induction of labour.
Women with gestational diabetes are also at increased risk of having a baby with a low blood glucose level after delivery. This is because of the sudden withdrawal of the mother’s high glucose supply and the baby’s relatively high insulin level. For this reason, together with additional concerns, the baby may need to be admitted to a special care nursery. These complications are directly related to the higher blood glucose levels in the mother. The good news is that they are highly unlikely if the diabetes is properly managed and blood glucose levels are kept relatively normal.
Finally, gestational diabetes is now a concern because of ‘programming’ in the womb and the potential for your baby to be more at risk of developing diseases in later life. What you eat during pregnancy affects the way the baby develops and the food choices that your baby will make later in life. It is not just your blood glucose levels that are important but all aspects of the diet. However, because carbohydrates are responsible for the rise and fall in your blood glucose levels after eating, carbohydrate foods are given special attention. Foods with a low GI will lead to a smaller rise and fall in the glucose levels and these gradual changes are passed through the placenta to the baby. Foods with a high GI will cause a rapid rise in your blood glucose and this glucose spike is passed through to the baby. For complex reasons related to the circulation of the amniotic fluid, this spike can have a sustained effect.
In September GI News, I’ll look at the risk factors for gestational diabetes.
This is an edited extract from my new book (with Dr Kate Marsh and Prof Robert Moses), The Bump to Baby Low GI Eating Plan for Conception, Pregnancy and Beyond (Hachette Australia). In the book we share the latest science to help women enjoy a healthy pregnancy while safeguarding their baby’s future wellbeing. It’s available from bookshops and online in Australia and NZ and as an eBook from Amazon, iTunes etc. We have a website too, where you can visit us, learn more about our book (and look inside), find pregnancy friendly recipes, keep up to date with the latest news about the importance of lifestyle for pregnancy and preconception, download information and weight charts, contact us and link to other useful information. Visit us HERE. 
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