Gestational diabetes mellitus (GDM) can be defined as “development of any degree of glucose intolerance, which is recognized for the first time during present pregnancy” and occurs is approximately 4% of all pregnancies. Most women who develop diabetes generally revert to normal after delivery and a few continues to have glucose intolerance, even after delivery and continues to have diabetes. Even those who revert to normal from gestational diabetes after delivery have high risk of developing diabetes in later life and 30%-60% of women with gestational diabetes eventually develop diabetes in later life.

The prevalence of gestational diabetes varies in different race and ethnic groups. The variation in the prevalence of gestational diabetes in different races and ethnic groups may be due genetic predisposition as well as different criteria and screening regimens used for detection of gestational diabetes.

The diagnosis of gestational diabetes is done the same way as done for general population. Oral Glucose Tolerance Test (OGTT) is done to diagnose gestational diabetes mellitus. Fasting plasma glucose of 126 mg/dl or more or random blood glucose of more than 200 mg/dl is considered diagnostic for gestational diabetes, the same criteria for general population. OGTT is done for high risk pregnancies for screening and glucose challenge test (GCT) is done in low risk pregnancies. OGGT is done in low risk pregnancies only if the GCT is above threshold level.

Screening for gestational diabetes:

Oral Glucose Tolerance Test (OGTT) in every pregnant woman may not be cost effective and to diagnose maximum number of gestational diabetes in pregnant women screening is done. The pregnant women are selected as high risk of gestational diabetes using the following criteria:

• Obesity.
• Age of pregnant woman more than 25 years.
• A family history of diabetes.
• Have polyhydramnios (excess amniotic fluid).
• History of previous pregnancy with complication such as big baby, still birth, or a child with a birth defect.
• History of glucose intolerance.
• If pregnant woman belong to a racial group with high prevalence of gestational diabetes.

Any pregnant woman with any (one or more) of the above criteria should undergo OGTT at the first prenatal visit and if the OGTT is negative for diabetes it should be repeated at 24-28 weeks of gestation.

Infants born to mothers with gestational diabetes are at higher risk of developing several chemical imbalances, such as low serum calcium and low serum magnesium levels. There are two major problems of infants born to gestational diabetes mothers, hypoglycemia and macrosomia.

Hypoglycemia:

Infants of gestational diabetes mother may suffer from hypoglycemia (low blood sugar level) immediately after delivery. In case of untreated (or sub-optimally treated gestational diabetes) gestational diabetes the mother has consistent high blood glucose level and as a result the fetus has high circulating insulin level. Even after delivery there may be high level of insulin in the infant, which results in hypoglycemia. The blood sugar level of the babies of gestational diabetes mother should be tested immediately after delivery and if found low, glucose should be supplied intravenously immediately.

Macrosomia:

Macrosomia is considerably larger baby in compare to normal babies. If mother’s blood glucose is consistently high the fetal pancreas secretes more insulin to metabolize excess glucose and converts glucose to fat which is than stored. Due to high glucose supply from maternal blood and high level of fetal insulin (fetus produces all the insulin it needs), large quantity of fat is deposited, resulting in a lager than normal baby.

NB: The above mentioned definition of gestational diabetes mellitus has limitations, although it has standardized the diagnosis of gestational diabetes. The limitation of the above definition of gestational diabetes is that the definition does not take into account if the pregnant woman had diabetes before pregnancy. The International Association of Diabetes and Pregnancy Study Group (IADPSG) has recommended to make the diagnosis of diabetes and not gestational diabetes mellitus, be made in pregnant women if the diabetes is diagnosed using the same standard diagnostic criteria which is used for general population.