Gestational Diabetes Mellitus (GDM)
What is Gestational Diabetes Mellitus?
Gestational diabetes occurs when the body is not able to make enough insulin, resulting in unstable blood sugars. The worldwide prevalence of gestational diabetes mellitus is on the rise. Approximately 3% to 20% of pregnant people develop GDM during pregnancy, depending on their risk factors.
Maternal risk factors for developing GDM include (Diabetes Canada 2018):
- Being 35 years old or older
- Being from a high risk ethnic group: African, Arab, Asian, Hispanic, Indigenous, and South Asian
- Using corticosteroid medication
- Having any of the following:
- Obesity (BMI 30kg/m2 or higher)
- GDM in previous pregnancy
- Birthed a previous baby 4kg or larger
- A parent, brother or sister with Type 2 diabetes
- Polycystic ovary syndrome
- Acanthosis nigricans
After a GDM diagnosis, the risks of the following increase (SOGC 2019): pre-eclampsia, shoulder dystocia, large for gestational age (LGA) baby, stillbirth, pregnant person’s risk of developing Type 2 diabetes later in life.
Both Diabetes Canada and the Society of Obstetricians and Gynaecologists of Canada (SOGC) recommend offering all pregnant people screening for GDM between 24- 28 weeks of pregnancy. Screening for GDM can occur in two ways:
- Glucose Challenge Screening Test (GCT)
- GCT is the standard non-fasting method of screening for GDM
- Involves drinking 50g of glucose
- Plasma glucose is measured one hour later (blood sample)
- If the value is under 7.8 mmol/L, no further testing is required
- If the value is 7.8 – 11.0 mmol/L an OGTT is required
- If the value is over 11.0 mmol/L GDM is diagnosed
- Oral Glucose Tolerance Test (OGTT)
- OGTT is the fasting diagnostic test for GDM
- Involves drinking 75g of glucose
- Plasma glucose is measured at fasting, 1 hour and 2 hours. If one of the following values is met or exceeded GDM is diagnosed
- Fasting: greater than or equal to 5.3 mmol/L
- 1 hour: greater than or equal to 10.6 mmol/L
- 2 hour: greater than or equal to 9.0 mmol/L
If you have risk factors for GDM, your midwife may suggest going directly for the OGTT instead of the GCT. In this case, the values for diagnosing GDM vary slightly. If one of the following values is met or exceeded, GDM is diagnosed.
- Fasting: greater than or equal to 5.1 mmol/L
- 1 hour: greater than or equal to 10.0 mmol/L
- 2 hour: greater than or equal to 8.5 mmol/L
How does being diagnosed with GDM impact your midwifery care?
Your midwife will consult with an OB with regards to your care after a GDM diagnosis. Depending on the management plan for your GDM and the individual OB, your most responsible provider may change (MRP). The MRP is the provider most responsible for your care, making the decisions about your care plan. Regardless of who is MRP, your midwife will still be present for the birth of your baby and provide the same level of postpartum care. For more details regarding your individual care, please ask your midwife.