Gestational diabetes mellitus (GDM) affects between 3% and 20% of pregnant women. It presents with a rise in blood glucose (sugar) levels toward the end of the 2nd and 3rd trimester of pregnancy. In 90% if cases, it disappears after the birth, but the mother is at greater risk of developing type 2 diabetes in the future.


It occurs when cells become resistant to the action of insulin, which is naturally caused during pregnancy by the hormones of the placenta. In some women, the pancreas is not able to secrete enough insulin to counterbalance the effect of these hormones, causing hyperglycemia, then diabetes.


Pregnant women generally have no apparent diabetes symptoms. Sometimes, these symptoms occur:

  • Unusual fatigue
  • Excessive thirst
  • Increase in the volume and frequency of urination
  • Headaches

Importance of screening

These symptoms can go undetected because they are very common in pregnant women.

Women at risk

Several factors increase the risk of developing gestational diabetes:

  • Being 35 years of age or older
  • Being overweight
  • Family members with type 2 diabetes
  • Having previously given birth to a baby weighing more than 4 kg (9 lb)
  • Gestational diabetes in a previous pregnancy
  • Belonging to a high-risk ethnic group (Aboriginal, Latin American, Asian, Arab or African)
  • Having had abnormally high blood glucose (sugar) levels in the past, whether a diagnosis of glucose intolerance or prediabetes
  • Regular use of a corticosteroid medication
  • Suffering from polycystic ovary syndrome (PCOS)
  • Suffering from ancanthosis nigricans, a discoloration of the skin, often darkened patches on the neck or under the arms


The Canadian Diabetes Association 2018 Clinical Practice Guidelines for the Prevention and Treatment of Diabetes in Canada recommends diabetes screening for all pregnant women, between the 24th and 28th week of pregnancy. Women with a higher risk of developing gestational diabetes should be tested earlier.
Two screening methods:
1. Most centres use a method done at two separate times. It begins with a blood test measuring blood glucose (sugar) levels 1 hour after drinking a sugary liquid containing 50 g of glucose, at any time of day. If the result is:

  • Below 7.8 mmol/L, the test is normal.
  • Above 11.0 mmol/L, it is gestational diabetes.
  • If it is between 7.8 and 11.0 mmol/L, the attending physician will ask for a second blood test measuring fasting blood glucose (sugar) levels, then for blood tests taken 1 hour and 2 hours after drinking 75 g of glucose. This will confirm gestational diabetes if the values are equal to or greater than:
  • 5.3 mmol/L fasting
  • 10.6 mmol/L 1 hour after drinking the sugary liquid
  • 9.0 mmol/L 2 hours after drinking the sugary liquid

2. The second method the oral glucose tolerance test (OGTT), with a sweetened liquid containing 75 g of glucose and three blood tests. A diagnosis is made if at least one of the three blood tests has values equal to or greater than:
5.1 mmol/L fasting
10 mmol/L 1 hour after drinking the sugary liquid
8.5 mmol/L 2 hours after drinking the sugary liquid

Risks and possible complications

There are numerous risks when gestational diabetes is not properly controlled and blood glucose (sugar) levels remain high.
For the mother:

  • Excess amniotic fluid, increases the risk of premature birth
  • Risk of caesarean section or a more difficult vaginal birth (because of the baby’s weight, among other reasons)
  • Gestational hypertension or preeclampsia (high blood pressure and swelling)
  • Higher risk of staying diabetic after the birth or of developing type 2 diabetes in the future (a 20% to 50% risk within 5 to 10 years of the birth).

For the baby:

  • Bigger than normal at birth (more than 4 kg of 9 lb)
  • Hypoglycemia (drop in blood sugar levels) at birth
  • Risk of the baby’s shoulders getting stuck in the birth canal during the birth
  • Risk of obesity and glucose intolerance in early adulthood (especially if birth weight was above 4 kg or 9 lb)

Slight risk of:

  • Jaundice, especially if the baby is premature
  • Lack of calcium in the blood
  • Breathing problems

Proper diabetes control considerably reduces the risks of complications.


When gestational diabetes is diagnosed, a personalized meal plan should be developed to control the mother’s glycemia
Generally, a healthy diet with proper portion control and distribution of carbohydrates (sugars), as well as a healthy lifestyle (stress management, enough sleep and physical activity), are sufficient to control gestational diabetes.
If blood glucose (sugar) levels remain too high, the physician will prescribe insulin injections or, in some cases, oral antidiabetics.
Target blood glucose (sugar) levels for the majority of pregnant women:

  • Fasting <5.3 mmol/L
  • 1 hour after a meal <7.8 mmol/L
  • 2 hours after a meal <6.7 mmol/L

The target values for controlling gestational diabetes differ from those of other types of diabetes.

Importance of a balanced diet

A balanced diet is essential for the control of blood glucose (sugar) levels and for a healthy pregnancy. When there is gestational diabetes, certain modifications need to be made to the mother’s diet, including to the amount of carbohydrates in each meal. A carbohydrate-controlled diet is the foundation of the treatment. It is essential not to eliminate carbohydrates completely but rather to distribute them throughout the day.

Your meal plan

A dietitian will help you establish or modify your meal plan based on your energy needs. The dietitian will also advise you about the important nutrients to incorporate in your diet during your pregnancy:

  • protein
  • essential fatty acids
  • iron
  • folic acid
  • vitamin D
  • calcium

For more information about balanced meals, consult the balanced plate.

Importance of being physically active

Physical activity helps control diabetes during pregnancy and has numerous health benefits for pregnant women.
It is recommended that most pregnant women do a total of 150 minutes of physical activity per week, ideally in at least 3 to 5 sessions of 30 to 45 minutes each. If you weren’t active before your pregnancy, start gradually.
Safe cardiovascular activities (done at light to moderate intensity) during pregnancy include:

  • walking
  • dancing
  • bicycling
  • swimming
  • stationary exercise equipment
  • cross-country skiing
  • jogging

Consult your doctor before starting these activities and avoid physical activities where you risk falling, losing your balance or have sudden changes in direction (for example: soccer, badminton, etc.).
Stay well hydrated before, during and after exercise, in addition to having with you at all times your blood glucose (sugar) meter and a source of rapidly absorbed carbohydrates in case of hypoglycemia.
Before engaging in physical activity, your insulin dosage may have to be reduced to limit the risk of hypoglycemia. Your medical team will help you adjust your dosage as required.

During the birth

During the birth, the medical team regularly monitors the mother’s blood glucose (sugar) levels and adjusts treatment based on the readings. The baby’s blood glucose (sugar) levels are also monitored in the hours following the birth.

After the birth

In the majority of cases, the diabetes disappears after the birth. However, the risk of developing diabetes in the future increases, especially if you keep your excess weight. To avoid this situation, you should maintain a healthy weight, eat a balanced diet and exercise regularly.
Furthermore, it is recommended that you have a blood glucose (sugar) test between 6 weeks and 6 months after the birth to check whether your blood glucose (sugar) levels have returned to normal values. Before getting pregnant again, you should consult a doctor.


Breastfeeding is recommended for all women, diabetic or not. Mother’s milk is an excellent food for your infant. Breast feeding not only helps the mother lose the weight gained during pregnancy, it also reduces blood pressure and helps control blood glucose (sugar) levels and thus prevent type 2 diabetes. It also reduces the risk of obesity and diabetes later on in the child. The nutritional needs of nursing mothers are essentially the same as in the last trimester of pregnancy.
It is recommanded to start breastfeeding immediately after birth to prevent hypoglycemia in the newborn, and to continue for a minimum of 6 months.

Other resources


    External resources

      Research and writing : Diabetes Québec’s team of health professionals

      September 2020

      © Diabetes Québec

      References :

      Feig D, Berger H, Donovan L et al. Diabetes Canada 2018 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada: Diabetes and Pregnancy. Can J Diabetes 2018; 42 (Suppl 1): S255-S282.

      Société canadienne de pédiatrie (28 février 2018). Le sevrage de l’allaitement [En ligne]. Repéré à (page consultée le 18 juillet 2018).