Diabetes - Gestational
Definition
Depending on the specific population, abnormal maternal glucose regulation occurs in 3-10% of pregnancies. Recent studies suggest that the prevalence of diabetes among women of childbearing age is increasing in the Western countries. This increase is believed to be attributable to (1) more sedentary lifestyles, (2) changes in diet, (3) continued immigration from high-risk populations, and (4) the virtual epidemic of childhood and adolescent obesity presently evolving.
Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance with onset or first recognition during pregnancy. Untreated GDM can lead to foetal macrosomia, hypoglycaemia, hypocalcaemia, and hyperbilirubinaemia. In addition, mothers with GDM have increased rates of caesarean delivery and chronic hypertension. To screen for GDM, a 50g glucose screening test should be done at 24-28 weeks of gestation. This is followed by a 100g, 3-hour oral glucose tolerance test if the patient's plasma glucose concentration at 1 hour during screening is greater than 7.8 mmol/L.
Normalisation of glucose levels in women with gestational diabetes will reduce the risk of complications such as macrosomia, birth trauma, need for caesarean section, and neonatal hypoglycaemia. If diet modification fails to improve glucose values, insulin therapy is indicated. Oral hypoglycaemic agents are contraindicated during pregnancy. Subsequent pregnancies can be affected, and the risk of developing type 2 diabetes is increased. If maternal glucose levels are uncontrolled, the infant can suffer CNS defects, macrosomia, organomegaly, cardiac or renal anomalies, situs inversus, asphyxia, respiratory distress, increased blood volume, hyperviscosity, congestive heart failure, hypocalcaemia, hypomagnesaemia, hypoglycaemia, or hyperbilirubinaemia, or the child may be stillborn.
Aetiology / Risk Factors
- Family history of type 2 diabetes: having a first-degree relative with type 2 diabetes leads to lifetime risk of 40%; similarly 25% to 33% of all type 2 diabetics have a family history of the condition.
Age older than 40 years
Excess body fat, particularly truncal obesity with waist circumference >88 cm
Sedentary lifestyle with diet high in fats and calories
Glucose intolerance, dyslipidaemia, hypertension
History of gestational diabetes
History of polycystic ovarian syndrome
Aboriginal or Torres Strait Islander, Pacific Islander, Indian or Chinese, African American, Hispanic American, and Native American descent.
Low birth weight and/or malnutrition in pregnancy may cause metabolic abnormalities in a foetus that later lead to diabetes.
Symptoms & Signs
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GDM only occurs during pregnancy. The diagnosis is established by glucose tolerance testing. The best method for diagnosing GDM continues to be controversial. The 2-step system is currently recommended in the United States. A 50g, 1-hour screening test is administered to all pregnant women at 26-28 weeks', followed by a 100g, 3-hour OGTT for those with an abnormal screening result. Alternatively, a 1-step, 75-g, 2-hour test can be administered. Other measurements (e.g., maternal HbA1C, random postprandial or fasting blood sugar level, fructosamine level) are not recommended because of low sensitivity.
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OGTT prerequisites for gestational diabetes are as follows:
One-hour, 50g glucose challenge result greater than 7.8 mmol/L
Overnight fast of 8-14 hours
Carbohydrate loading for 3 days (>150 g carbohydrates)
Seated and not smoking during the test
Two or more values met or exceeded
Either a 2-hour (75 g of glucose) or 3-hour (100 g of glucose) test