Michael R. Virro, MD, FRCSC.

Gestational diabetes is one of the more common disorders in pregnancy, affecting approximately 7-15% of pregnant women.  It is defined as any degree of glucose intolerance that is first diagnosed during pregnancy.

DIAGNOSIS: Pregnant women should be interviewed carefully during the first prenatal visit to assess the potential risk for gestational diabetes.  Patients with marked obesity or a personal/ family history of diabetes should be considered at high risk.  Conversely, patients that are less than 25 years of age, have a normal pre-pregnancy weight and have no family history of diabetes are considered to be low risk.  It can be argued that all patients should be screened for diabetes in pregnancy.  If this is not possible, patients can be assessed for clinical characteristics suggestive of diabetes.  At our clinic, we screen all normal-risk patients for gestational diabetes between 24-28 weeks gestation with a 1 hour 50 gm Oral Glucose Challenge Test (OGTT).  The pregnant woman drinks a sweet drink then has a blood test one hour later. A blood glucose value of >7.8 mmol/l following a 50 gm glucose load is suggestive of gestational diabetes and will identify approximately 80% of patients that will eventually develop gestational diabetes.  If the 1 hour test is abnormal, the patient is instructed to have a 100 gm OGTT.  For this test, the patient fasts overnight and has a blood test the next morning to determine the sugar level in the blood (fasting blood sugar). She then ingests the 100 gm sugar drink, and has glucose levels taken at 1, 2 and 3 hours following ingestion of the drink.  Two abnormally elevated glucose levels are diagnostic of gestational diabetes.  A diagnosis of gestational diabetes can be made when a fasting blood sugar is > 7.0 mmol/l or a random glucose level is > 11.1 mmol/l.


IMPLICATIONS: Non-treated elevated glucose levels can lead to both obstetric and birthing complications.  Untreated high blood glucose levels can lead to a higher incidence of fetal distress in labour and there is a slightly higher incidence of stillbirth infants in the last trimester of pregnancy.  As blood glucose levels increase, women have a higher chance of developing hypertensive disorders and there is a higher incidence of fetal macrosomia (larger babies).  Larger babies may lead to more operative deliveries including vacuum assisted deliveries, the use of forceps or the need for cesarean section.  Babies delivered from diabetic mothers have a higher incidence of perinatal unit admissions because of hypoglycemia (low blood sugar), jaundice and hypocalcemia (low calcium).


TREATMENT: Treatment of Gestational Diabetes is usually successful through proper dietary counseling and exercise. Individualization of nutritional needs is based on the patient’s weight and blood glucose levels.  Caloric intake may need to be reduced significantly in obese women.  A reduction in carbohydrate levels to 35 – 40% of total caloric intake has been shown to decrease maternal glucose levels and improve maternal and fetal outcomes.  For patients that do not respond to conventional treatment with diet and exercise, insulin is the drug of choice to reduce maternal glucose levels and subsequent fetal morbidity.  The dosage and administration of insulin is primarily dependent on maternal glucose levels in conjunction with assessment of fetal growth characteristics.

OBSTETRICAL MONITORING:  Starting in the 3rd trimester of pregnancy, aside from monitoring blood glucose levels, patients with gestational diabetes need close maternal surveillance of blood pressure and monitoring the presence of protein in the urine to detect hypertensive disorders.  Weekly non-stress testing and serial ultrasounds, including biophysical profile, can be used to monitor fetal well-being including fetal growth, amniotic fluid level, fetal movement and tone.

As a general rule, women with gestational diabetes usually have their labour induced prior to 40 weeks gestation if they have not gone into labour spontaneously.  Induction of labour primarily depends on how many children/ pregnancies the new mother has had and the status of her cervix.  Induction of labour through Prostaglandin gels and oxytocin are not contraindicated in women with gestational diabetes.

AFTER BIRTH: Blood glucose levels will usually revert back to normal after birth.  Assuming blood glucose levels are normal six weeks post-delivery, blood glucose monitoring should be assessed at a minimum of 3-year intervals.  Women with an abnormal blood glucose level 6 weeks post partum should be tested for diabetes on an annual basis.  All patients diagnosed with gestational diabetes should be educated regarding lifestyle modifications to maintain an ideal body weight through both diet and an exercise program.   Patients should be educated in maintaining ideal glucose levels prior to a subsequent pregnancy.  Optimal blood sugar control prior to and during pregnancy will lessen any potential obstetric and perinatal complications considerably.

Women with gestational diabetes are at a higher risk of developing diabetes later in life.  The children delivered from diabetic mothers also have an increased risk of obesity, glucose intolerance and diabetes either in late adolescence or young adulthood.  Women diagnosed with gestational diabetes may still use oral contraceptive birth control pills following delivery as long as there are no other medical contraindications to the birth control pill that exist.


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