Gestational Diabetes

“Risk factor: up to one in four pregnancies! depending on the region.”

Gestational Diabetes Mellitus (GDM) is the one which affects females during pregnancy. It is typically diagnosed during the pregnancy and the majority of women can control it simply with exercise and diet.

Gestational Diabetes generally has few symptoms and it is most commonly diagnosed by screening during pregnancy. Diagnostic tests detect inappropriately high levels of glucose in blood samples.

Gestational Diabetes resembles Type 2 Diabetes in several respects, however typically it will disappear after the baby is born.

In most of cases (75–90%), Gestational Diabetes is a condition in which women without previously diagnosed Diabetes exhibit high blood glucose (blood sugar) levels during pregnancy (especially during their third trimester).

Gestational Diabetes is caused by improper insulin responses. This is likely due to pregnancy-related factors such as the presence of human placental lactogen that interferes with susceptible insulin receptors. This in turn causes inappropriately elevated blood sugar levels.

Scientists from the National Institutes of Health and Harvard University published a very interesting study whereby they found that women whose diets before becoming pregnant were high in animal fat and cholesterol had a higher risk for gestational Diabetes, compared to their counterparts whose diets were low in cholesterol and animal fats.

Typical risk factors and risk markers for women:

  • age (the older a woman of reproductive age is, the higher her risk of Gestational Diabetes)
  • overweight or obesity
  • excessive weight gain during pregnancy
  • a family history of Diabetes
  • Gestational Diabetes during a previous pregnancy
  • a history of stillbirth or giving birth to an infant with congenital abnormality
  • and excess glucose in urine during pregnancy

The frequency of previously undiagnosed Diabetes in pregnancy and gestational Diabetes varies among populations but probably affects 10–25% of pregnancies, which means up to one in four pregnancy.

It has been estimated that most (75–90%) cases of high blood glucose during pregnancy are gestational Diabetes.

Some women have very high levels of glucose in their blood, and their bodies are unable to produce enough insulin to transport all of the glucose into their cells, resulting in progressively rising levels of glucose.

Between 10% to 20% of pregnant women with Gestational Diabetes will need to take some kind of blood-glucose-controlling medications.

Undiagnosed or uncontrolled Gestational Diabetes can raise the risk of complications during childbirth. As with Diabetes Mellitus in pregnancy in general, babies born to mothers with untreated gestational Diabetes are typically at increased risk of problems such as being large for gestational age (which may lead to delivery complications), low blood sugar, and jaundice.

If untreated, it can also cause seizures or stillbirth. Not to mention the direct risk for the infant, since the baby can be bigger than he/she should be.

Generally speaking the Diabetes in pregnancy and Gestational Diabetes increase the risk of future obesity and Type 2 Diabetes in offspring.

However Gestational Diabetes is a treatable condition and in 90% of the cases women can control it simply with exercise and diet. The food plan is often the first recommended target for strategic management of Gestational Diabetes.

Treatment of Gestational Diabetes is also important because women with unmanaged Gestational Diabetes are at increased risk of developing Type 2 Diabetes Mellitus (or very rarely, LADA or Type 1) after pregnancy.

A woman is diagnosed with Gestational Diabetes when glucose intolerance continues beyond 24–28 weeks of gestation.

There is also a classification available for Gestational Diabetes, called “White classification”. It was named after Priscilla White who pioneered research on the effect of Diabetes types on perinatal outcome, it is widely used to assess maternal and fetal risk.

The White classification distinguishes between Gestational Diabetes (Type A) and Pre-Gestational Diabetes (Diabetes that existed prior to pregnancy).

These two groups are further subdivided according to their associated risks and management.

The two subtypes of Gestational Diabetes under this classification system are:

  • Type A1: abnormal Oral Glucose Tolerance Test (OGTT), but normal blood glucose levels during fasting and two hours after meals; diet modification is sufficient to control glucose levels.
  • Type A2: abnormal Oral Glucose Tolerance Test compounded by abnormal glucose levels during fasting and/or after meals; additional therapy with insulin or other medications is required.

Diabetes which existed prior to pregnancy is also split up into several subtypes under this system:

  • Type B: onset at age 20 or older and duration of less than 10 years.
  • Type C: onset at age 10–19 or duration of 10–19 years.
  • Type D: onset before age 10 or duration greater than 20 years.
  • Type E: overt Diabetes Mellitus with calcified pelvic vessels.
  • Type F: diabetic nephropathy.
  • Type R: proliferative retinopathy.
  • Type RF: retinopathy and nephropathy.
  • Type H: ischemic heart disease.
  • Type T: prior kidney transplant.

An early age of onset or long-standing disease comes with greater risks, hence the first three subtypes.

The precise mechanisms underlying Gestational Diabetes remain unknown. The hallmark of Gestational Diabetes is increased insulin resistance. Pregnancy hormones and other factors are thought to interfere with the action of insulin as it binds to the insulin receptor. The interference probably occurs at the level of the cell signaling pathway behind the insulin receptor.

Since insulin promotes the entry of glucose into most cells, insulin resistance prevents glucose from entering the cells properly. As a result, glucose remains in the bloodstream, where glucose levels rise. More insulin is needed to overcome this resistance; about 1.5–2.5 times more insulin is produced than in a normal pregnancy.

Though the clinical presentation of Gestational Diabetes is well characterized, the biochemical mechanism behind the disease is not well known.

It is unclear why some women are unable to balance insulin needs and develop Gestational Diabetes; however a number of explanations have been given, similar to those in Type 2 Diabetes: autoimmunity, single gene mutations, obesity, along with other mechanisms.

A number of screening and diagnostic tests have been used to look for high levels of glucose in plasma or serum in defined circumstances.

One method is a stepwise approach where a suspicious result on a screening test is followed by diagnostic test.

Alternatively, a more involved diagnostic test can be used directly at the first prenatal visit for a woman with a high-risk pregnancy.

Non-challenge blood glucose tests involve measuring glucose levels in blood samples without challenging the subject with glucose solutions.

A blood glucose level is determined when fasting, 2 hours after a meal, or simply at any random time. In contrast, challenge tests involve drinking a glucose solution and measuring glucose concentration thereafter in the blood; in Diabetes, they tend to remain high.

The glucose solution has a very sweet taste which some women find unpleasant; sometimes, therefore, artificial flavours are added. Some women may experience nausea during the test, and more so with higher glucose levels.

Criteria for diagnosis of Gestational Diabetes, using the 100 gram Glucose Tolerance Test, according to Carpenter and Coustan:

Gestational Diabetes (Carpenter and Coustan)
  • Fasting blood glucose level ≥95 mg/dl (5.33 mmol/L)
  • 1 hour blood glucose level ≥180 mg/dl (10 mmol/L)
  • 2 hour blood glucose level ≥155 mg/dl (8.6 mmol/L)
  • 3 hour blood glucose level ≥140 mg/dl (7.8 mmol/L)

Criteria for diagnosis of gestational Diabetes according to National Diabetes Data Group:

Gestational Diabetes (National Diabetes Data Group)
  • Fasting blood glucose level ≥105 mg/dl (5.8 mmol/L)
  • 1 hour blood glucose level ≥190 mg/dl (10.6 mmol/L)
  • 2 hour blood glucose level ≥165 mg/dl (9.2 mmol/L)
  • 3 hour blood glucose level ≥145 mg/dl (8.1 mmol/L)

The glucose values used to detect Gestational Diabetes were first determined by O’Sullivan and Mahan (1964) in a retrospective cohort study (using a 100 grams of glucose OGTT) designed to detect risk of developing Type 2 Diabetes in the future.

The values were set using whole blood and required two values reaching or exceeding the value to be positive. Subsequent information led to alterations in O’Sullivan’s criteria. When methods for blood glucose determination changed from the use of whole blood to venous plasma samples, the criteria for Gestational Diabetes were also changed.

And finally a very important thing to remember. It is a proven fact that Gestational Diabetes signals future Diabetes risk not only in mothers, but also in fathers.


Researched, collected and written by Zsolt Szemerszky

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