gestational diabetes

Diabetes in pregnancy

Blood glucose control is vital during pregnancy. This control is necessary because abnormal blood sugars can harm your baby. Women with pre-existing diabetes need monitoring from very early in their pregnancy, and their diabetes specialist plays an essential role in their health care team. Uncontrolled blood sugars early in your pregnancy can cause congenital disabilities and miscarriage.

Women who develop diabetes during their pregnancy (gestational diabetes, or GDM) also require specialist management, so that excessive blood sugar does cause problems for their growing baby. GDM usually goes away after the baby is born.

GDM happens because your placenta produces hormones to help your baby grow and develop. However, these hormones block the action of the mother’s insulin. This ‘resistance’ is normal and results in a 2-3-fold increase in the need for insulin during pregnancy.

If insulin resistance is already a problem for you, your body may not be able to cope with a higher need for insulin.  Your blood glucose levels (BGL’s) will be high, resulting in a GDM diagnosis.

Testing for gestational diabetes is recommended at around week 28; however, if you have any risk factors, your care provider may suggest earlier testing. We don’t yet know what causes GDM, but we do know you are at a higher risk of developing it if you:

  • Have a family history of gestational diabetes (14)
  • Are over 25 years of age
  • Have a family history of type 2 diabetes
  • Are overweight
  • Have had gestational diabetes during previous pregnancies
  • Are from an Indigenous Australian or Torres Strait Islander background
  • Have previously had Polycystic Ovary Syndrome
  • Are from a Vietnamese, Chinese, Middle Eastern, Polynesian or Melanesian background
  • Have previously given birth to a large baby

Testing for gestational diabetes

Traditionally there have been two tests used to diagnose GDM. The short test – called the Glucose Challenge Test (GCT) – is when a blood sample is taken 1 hour after a special glucose drink to see how your body handles the sugar.

If these test results are abnormal, then a follow-up test called Oral Glucose Tolerance Test (OGTT or GTT) is done. In this test, we take blood before the drink, one hour and two hours after the drink. The GTT is the gold-standard test for diagnosing GDM. Many services no longer recommend the shorter GCT.

Most women with diabetes in pregnancy have an otherwise straightforward pregnancy, normal delivery and a healthy baby when they manage their blood glucose levels (BGL’s) well. To ensure the best possible outcome, we refer women with GDM to a specialist team for the management of their diabetes during pregnancy. These may be an endocrinologist (doctor specialising in diabetes), a dietician and a diabetes educator.

Managing your diabetes

Healthy eating, regular physical activity and proper monitoring of your BGL’s are vital to the management of blood glucose. Women for who diet and exercise do not work may need medication to help them control their blood sugar. Approximately 10-20% of women with GDM will require insulin injections for the remainder of their pregnancy (15).

Attending appointments with your specialist team is vital in the management of your diabetes. During these reviews, you can discuss your glucose monitoring and the plan for keeping your BGL’s under control. They will help you understand how your body reacts to different situations and change your treatments to suit your needs as required. An essential part of managing gestational diabetes is your diet.

A healthy and balanced diet will assist to (15)

  • Manage your BGL’s and keep them within your target range
  • Provide optimal nutrition for both you and your baby
  • Ensure appropriate weight gain during your pregnancy.

Women with gestational diabetes are encouraged to:

  • Eat little and often, and maintain a healthy weight
  • Include some of the recommended carbohydrates in every meal and snack
  • Choose a variety of healthy and nutritious foods
  • Choose foods that are high in fibre
  • Avoid foods and drinks containing large amounts of sugar
  • Choose low glycaemic index (GI) carbohydrates

Consistently high glucose during pregnancy is toxic for baby and may result in miscarriage, premature delivery or stillbirth. Women and babies of mothers who develop GDM are also at a higher risk of type 2 diabetes later in life (16).

Staying active

For women with GDM, regular moderate physical activity can help to manage blood glucose levels. ‘Moderate’ means a slight but noticeable increase in breathing and heart rate. If there are no specific obstetric or medical risk factors, you should be able to exercise during pregnancy safely. However, it is best to discuss your activity level with your obstetrician or midwife before commencing any exercise regime in pregnancy.

How can gestational diabetes affect my baby?

If gestational diabetes is not well controlled and your BGL’s stay or are regularly high, it may result in problems for your baby. While a baby is still inside its mother, its system for processing glucose works just fine. It puts out enough insulin to cope with the amount of glucose it needs to process.

Babies exposed to large quantities of glucose (or sugar) may store it the same way as we do – in the form of fat. Therefore, GDM can result in very big (called macrosomic) babies a. A macrosomic baby can increase the risk of birth complications, instrumental birth and caesarean section.

Gestational diabetes can also create a need for baby to be looked after in special care to stabilise their BGL’s after birth. This instability happens because immediately after it is born, the baby’s insulin levels remain where they needed to be to process the glucose coming from the mother. However, after the baby is born, that glucose supply is cut off.

The insulin in the baby’s system keeps processing the baby’s glucose, sometimes to the point where the baby’s BGL’s end up too low. This condition is called hypoglycaemia. Your care provider will recommend monitoring your baby’s BSL’s by a small heel prick test regularly until they are stable. You can correct mild hypoglycaemia by ensuring your baby feeds regularly, at least until they can balance out their insulin levels.

Your baby’s blood sugar

Breastfeeding is the most effective natural way to stabilise your baby’s blood sugar levels. If your baby needs more support, there are other options. These include donated breastmilk, formula top-ups and glucose in baby’s mouth or through a drip into a baby’s vein.

While this might seem extreme, there are pros and cons to each option. While formula feeding may seem the easiest and quickest solution to the problem, it may not be the best for baby’s gut health. Please discuss your options and ensure you have all the necessary information to provide informed consent for any intervention.

Antenatal expressing

Antenatal expressing is the practice of hand expressing the early breastmilk (colostrum) before the birth of your baby. The colostrum is usually collected and stored in syringes with a special cap, labelled with date and time of collection and frozen. The stored colostrum is then defrosted during your birth, ready to feed your baby if there is a delay in initial breastfeeding.

Having a store of colostrum can be valuable, especially in the case of women with gestational diabetes (GDM). Babies born to women with GDM require frequent feeds to ensure baby’s blood glucose doesn’t drop below normal levels. Feeding this expressed milk in the first few hours after birth as a supplement to breastfeeds may support the baby to stabilise its sugars. It may also be useful under other circumstances. For example, women who want to breastfeed exclusively may choose to express breastmilk. That way if your baby doesn’t latch well or there is a delay in the first breastfeed, they still get colostrum.

What’s the evidence?

Historically, recommendations around antenatal expressing evolved from logic and word of mouth rather than substantial scientific evidence. In 2011-12 two studies looked at the birth outcomes for women expressing milk before their babies were born (17, 18).

These found that babies were more likely to be admitted to the special care nursery if their mothers had been advised to express antenatally. They were also born a week earlier than those born of mothers who did not.

These findings prompted many health services to stop recommending women express before the baby was born under all circumstances. A large study was then launched in Australia to research these connections further.

This study was conducted in women whose diabetes was controlled by either diet, medication or insulin with diabetes in pregnancy. They were otherwise low risk.

What are the findings?

The study reported that antenatal expressing from 36 weeks did not affect the risk of nursery admissions (19). That is, while it didn’t appear to increase the risk of babies admitted to the nursery, it also didn’t reduce the nursery admission rate. In other words, while it didn’t do any harm, it didn’t stop babies of GDM mums from needing nursery care.

The study also found that there was no significant difference between the preterm birth rate in expressing and non-expressing mums. In other words, no effect, harmful or beneficial.

What it did find was that babies of mothers who expressed and stored their colostrum were more likely to only be fed breastmilk in the first few weeks. However, This effect did not last beyond three months of age. These findings are of great value when we look at breastmilk and its role in long term infant health. It may act to establish the infants’ microbiome and protect the baby against future diabetes.

Dr Janelle McAlpine (PhD), Clinical Midwife
Photo by Ilya Kwangmoozaa, used under license from