Glucose testing – screening for gestational Diabetes

What is gestational diabetes?

Gestational diabetes (GD) is a type of diabetes that occurs during pregnancy. It happens when your body is not able to produce enough insulin to keep the amount of glucose (sugar) in your blood at proper levels. Untreated GD increases the likelihood of having a large baby, and is associated with birth complications as well as health risks for the newborn (e.g., preeclampsia, shoulder dystocia). Untreated GD also increases the risk of stillbirth late in pregnancy (36-40 weeks). Women who develop GD are at higher risk of developing type 2 diabetes in the future. However, there is excellent treatment for GD, and most women diagnosed with GD have normal deliveries and healthy babies.

Why is it important to screen for gestational diabetes?

All pregnant women should be offered blood glucose screening for GD between 24 and 28 weeks of pregnancy. If you have risk factors for GD, you will be tested earlier in your pregnancy. These risk factors include:

  • Being older than 35
  • Obesity (defined as a pre-pregnancy BMI greater than 30)
  • Aboriginal, African, Asian, Hispanic, or South Asian ethnicity
  • Family history of diabetes
  • Polycystic ovarian syndrome or acanthosis nigricans
  • Corticosteroid use during pregnancy
  • Previous pregnancy with GD
  • Previous delivery of a baby large than 4000 g

What does the blood glucose test involve?

All pregnant women are offered this screening test between 24-28 weeks gestation. When other risk factors are present, such as obesity, the test may be offered earlier and then repeated if initially normal. The screening test for GD is called a ‘glucose challenge’, which aims to see how your body is handling sugars. The measurement is taken 1 hour after you consume a glucose drink. This test can be conducted at any time of day as it is not a fasting test. If your blood sugar is normal after the challenge, you will not require any more testing. If it is high, you will have a second test. This test is done in the morning while you are fasting and will require you not to eat prior to the test. You will have your glucose tested before consuming a glucose drink and then tested again 1 and 2 hours later. If your glucose is higher than specific cut-off values, it means you have GD. See the table for more specific information.

Screening for gestational diabetes

Step 1 – non fasting, 50 g glucose challenge

1 hour Less than 7.8 mmol/L = no further testing
Between 7.8 and 11.1 mmol/L, go to step 2
Higher than 11.1 mmol/L = GD

Step 2 – fasting, 75 g glucose challenge


Higher than 5.3 mmol/L = GD
1 hour Higher than 10.6 mmol/L = GD
2 hour Higher than 9.0 mmol/L = GD

What if I have gestational diabetes?

GD is increasingly common, with about 7% of women having the condition. If you are found to have GD, you will work closely with your health care provider(s) to keep your blood glucose levels in a healthy range. This involves choosing a healthy diet, gaining the recommended weight during your pregnancy, getting exercise, and if needed, taking insulin or pills to lower your blood sugar. Your baby’s wellbeing will be carefully monitored by regular measurements of growth and amniotic fluid volume. If you have GD you will be offered a repeat glucose tolerance test between 6 weeks and 6 months postpartum to detect prediabetes and diabetes. You may also be offered induction between 38-40 weeks of pregnancy. Finally, it is strongly recommended that women with GD breastfeed their infants.