Gestational Diabetes Mellitus (GDM)

Gestational diabetes (GDM) is one of the most common medical complications of pregnancy. Characterised by glucose intolerance of varying severity, GDM develops or is first recognised mostly in the second or third trimesters (Nankervis & Conn 2013). GDM is largely determined by genetics and by your placenta, as high as 10-15% of all women aged 15-49 develop gestational diabetes, so is important to screen all women in pregnancy. Although you cannot “cause” GDM, there are known risk factors that increase your chance of developing.


Risk factors for GDM include:

  • Women age 40 years or over
  • Ethnicity (Aboriginal & Torres Strait Islander, Polynesian, Chinese, Southeast Asian, Middle Eastern or Indian backgrounds
  • Family history of type 2 diabetes or a first-degree relative (mother or sister) who has had gestational diabetes
  • Women above the healthy weight range prior to falling pregnant (BMI >30)
  • Women who have had elevated blood glucose levels in the past
  • Women with a previous history of gestational diabetes in pregnancy
  • Women with a history of Polycystic Ovary Syndrome (PCOS)
  • Women who have previously given birth to a large baby (>4.5kg)
  • Women taking some types of anti-psychotic or steroid medications
  • Women who gain weight too rapidly in the first half of pregnancy
  • Women pregnant with twins/triplets



A diagnosis of GDM is made by completing a Glucose Tolerance Test (GTT). If your blood glucose levels are above the recommended criteria considered ‘normal range’ (which have been endorsed by the World Health Organisation) you are diagnosed as having GDM. Your midwife or obstetrician at Hatch will provide you with an NDSS (National Diabetes Services Scheme) registration form which will enable you to purchase a glucometer and test strips from a chemist at a cheaper price to start monitoring your blood glucose levels before and after meals. They will also explain what the target ranges are and where you can access additional information. The news of being diagnosed with GDM can be upsetting. It is important to remember the majority of women with GDM go on to have a healthy pregnancy, birth and baby. Complications arise from miss diagnosis or undertreatment.


What are the effects for me and my baby?

Whilst GDM usually resolves after the baby is born, it is an important health issue which can have implications for both the mother and baby both in the short and long term.

When a mother’s body becomes resistant to the effects of insulin (the hormone that reduces blood sugar levels), the blood glucose levels remain high and the glucose passes through the placenta to the baby. In response to this, the baby produces higher levels of insulin, which is a growth hormone. Therefore, if GDM is not well managed, complications can arise from the baby growing too large, such as an increased risk of preterm birth or baby requiring admission to nursery to help with breathing or to manage low blood glucose, or jaundice.

Giving birth to larger babies can potentially cause more problems for the mother during their pregnancy and following birth such as an increased risk of developing preeclampsia, having their labour induced or requiring an instrumental birth. Additional long-term risks for mother is an increased incidence risk of developing GDM in another pregnancy or Type 2 diabetes later on in life.


Treatment of GDM

Managing GDM is a team effort involving you, your family, your maternity care team and additional health care professionals. You will have a modified schedule of visits at Hatch to include two additional obstetrician visits. Treatment involves dietary advice and education, an exercise and eating plan, close monitoring of your blood glucose levels (BGL’s), extra monitoring of baby’s growth during pregnancy and sometimes medication.

Most often lifestyle modifications including diet, exercise and blood sugar monitoring is enough to control GDM. Seeking advice on diet and nutrition is the first step. At Hatch we work closely with the team at Tree of Life Nutrition. Lisa and Desi will provide specialised dietary advice and tailor a meal plan with distribution of carbohydrates according to your blood glucose. They also work with exercise physiologists and a diabetes educator. Oral medication and/or insulin therapy is only required if blood sugar levels cannot be maintained in the optimum range. In this situation a referral will be made to see an endocrinologist in addition to your dietitian visits.


As diet is of the most importance to ensure appropriate fuel for both the mother and baby during pregnancy whilst also maintaining appropriate blood glucose levels. Lisa Peterson from Tree of life has provided a couple of general tips:

  • maintaining a healthy weight throughout pregnancy (your midwife will advise what is your optimal gestational weight gain in pregnancy at your first appointment)
  • choose a 1-2 serves of wholegrain carbohydrate at each meal
  • eat small meals regularly throughout the day
  • choose carbohydrate foods that are low in glycaemic index (GI index fact sheet)
  • avoid foods and drinks that are high in sugar (less than 10g sugar/100g) (Understand food labels fact sheet)
  • ensure enough fibre during the day. oats, wholegrains breads, legumes, psyllium husks, oat bran, legumes
  • choose foods that are nutrient dense: i.e. red meat, fish, chicken, legumes (iron), dairy (calcium), leafy vegetables (folate), nuts and seeds (mono and poly-unsaturated fats) as well as a variety from all other food groups.


Remember, complications from GDM arise from missing the diagnosis, under-treatment and the consequences of macrosomia (excessive growth of your baby). Therefore, testing positive provides an opportunity to educate regarding weight management and lifestyle modifications to reduce risks associated with glucose intolerance in later life and improves the outcome of your pregnancy.


For your additional understanding see below for some resources to better understand GDM and give you some ideas about diet: