Gestational diabetes mellitus (GDM) is defined as glucose intolerance diagnosed first during pregnancy in an otherwise non-diabetic woman. Presently, it has become a highly prevalent metabolic disorder of pregnancy.

With family histories of diabetes (a high-risk factor) on the rise, gestational diabetes is bound to increase its presence.

Testing or screening to diagnose gestational diabetes is an essential part of managing pregnancy in view of the dangerous complications this disorder can have, if not controlled. Medicine today lays stress on early diagnosis and prompt medical management.

New guidelines that define the criteria for diagnosis have been set. They will increase the prevalence of GDM by approximately 18%.

The purpose of testing is to provide better care for pregnant women with gestational diabetes, in an attempt to reduce its maternal and fetal complications.

Gestational diabetes mellitus (GDM) usually begins halfway through pregnancy and many a time it produces no symptoms. At times, when present, the symptoms will be mild in nature and likely to be missed.

Testing and diagnosis, therefore, become important. Just doing a blood sugar test or urine sugar test to determine blood glucose levels will not confirm gestational diabetes even if the test shows high blood sugar levels.

Test to diagnose gestational diabetes

Your doctor diagnoses gestational diabetes by screening with a test called the oral glucose tolerance test (OGTT) between 24 and 28 weeks of pregnancy. This is because GDM is a condition that develops usually in the second half of pregnancy.

The glucose tolerance test is the only test for gestational diabetes to confirm this type of diabetes.

A woman with high-risk factors may be advised this gestational diabetes test early on during pregnancy, maybe as soon as the pregnancy is confirmed. You should read about these risk factors to see where you stand.

Oral glucose tolerance test to diagnose GDM

The oral glucose tolerance test (OGTT) is performed by first taking your 8-hour fasting blood sample, usually the morning sample after an overnight fast. You are then given liquid or plain water, which contains 75 grams of glucose. Your body rapidly metabolizes this sugary drink and your blood sugar levels rise quickly.

One hour after you have drunk the glucose, your blood is again withdrawn and tested for blood glucose levels.

Another sample is drawn again after another hour and tested for glucose levels. If your blood glucose level is elevated above normal, one or more times during the test, you have gestational diabetes.

Criteria in the new guidelines of 2015

The American Diabetes Association has set the following criteria in the new guidelines of 2015 with relevant values.

Abnormal values (above normal limits) have been defined in women without pre-existing diabetes and with 75 gm glucose.

  • Fasting:  At or above 92 mg/dL (5.1mmol/l)
  • 1 Hour:  At or above 180 mg/dL (10.0mmol/l)
  • 2 Hour:  At or above 153 mg/dL (8.5mmol/l)

You may again be tested on another day with 100 grams of glucose, every hour over a three-hour period with a follow-up glucose tolerance test. If at least two samples show higher glucose levels, you will be diagnosed with gestational diabetes.

Values above the following are defined as high:

  • Fasting serum glucose of 95 mg/dl or 105 mg/dl (5.5/5.8 mmol/l)
  • 1-hour serum glucose of 180 mg/dl or 190 mg/dl (10.0 / 10.6 mmol/l)
  • 2-hour serum glucose of 155 mg/dl or 165mg/dl (8.6 / 9.2 mmol/l)
  • 3-hour serum glucose of 140 mg/dl or 145 mg/dl (7.8 /8.0 mmol/l)

Regular follow-up testing

Once you have confirmed your diagnosis of gestational diabetes, you should regularly test your blood by using a glucometer or glucose meter.

This is an electronic device, which you can use at home to find the approximate level of your blood glucose. You have to prick your finger with a needle or lancet.

You place a drop of the oozing out blood on a special strip, which you then insert into the glucose meter. This method helps to test your blood sugar in the comfort of your own home or even at your place of work

The American Diabetes Association recommends that all women with diagnosed gestational diabetes have a two-hour glucose tolerance test at six weeks and at least every three years after having given birth to rule out diabetes mellitus type 2.