Gestational Diabetes Diagnosis and Tests

Gestational Diabetes Diagnosis and Tests

Gestational diabetes is extremely common, occurring in 5-9 percent of pregnancies in the US.  It seems to be becoming more common in recent years.  Gestational diabetes is controversial.  Sources don’t seem to be able to agree on the guidelines for testing and treatment of the disorder.

Recent research has indicated that, when the gestational diabetes is adequately managed, there are benefits to both the mother and the newborn baby.  Some benefits in managing gestational diabetes include decreased chances of nerve palsies, fractures, and shoulder dystocia in the newborn. There are fewer cases of neonatal hypoglycemia (low blood sugar in the newborn) when the gestational diabetes has been managed.

The diagnosis of gestational diabetes is generally made by first giving the pregnant mother a 50-gram load of glucose in a sugary beverage and measuring the blood glucose levels after 1 hour.  If the test is abnormal, the mother is given the standard 3-hour glucose tolerance test, which clinches the diagnosis of the disorder.

In general, once the diagnosis is made, gestational diabetes treatment consists of dietary modification, glucose monitoring, increased exercise and sometimes the use of insulin in order to maintain the blood sugars during pregnancy.  Usually just insulin is used to manage the diabetes; however, some women are given metformin or glyburide in order to keep the blood sugars in good control.

In women who receive insulin or other therapy for gestational diabetes, non-stress tests are performed and indices of the amniotic fluid are begun in the third trimester of pregnancy in order to see whether or not the fetus is suffering from any type of stress as a result of being exposed to high levels of blood sugar in the womb.

Screening for Gestational Diabetes

According to the US Preventative Services Task Force (USPSTF) and the Cochrane Collaboration, there was no evidence to indicate whether or not women should be screened for gestational diabetes.  A recent study, however, indicated that, when pregnant women are screened for gestational diabetes and receive adequate treatment, there are benefits to treatment.

In addition, a more recent observational study indicated that high blood sugar in the mother led to elevated birth weight in the infant.  This lends further credence to the idea that pregnant women should be screened for gestational diabetes and managed once the diagnosis of gestational diabetes has been made.

Gestational diabetes involves blood glucose elevations and insulin intolerance beginning in the late second to early third trimesters of pregnancy. In the US, more than 90 percent of obstetrical practices advocate for the screening of the disorder, according to a poll by the American College of Obstetricians and Gynecologists (ACOG).  Most women are tested for the disorder, although there is a small subset of women who may be able to avoid getting screened for gestational diabetes in pregnancy.

While most women should be screened for gestational diabetes at 24 weeks’ gestation, those women with risk factors for the disease should be screened earlier.  Risk factors for gestational diabetes include having a first degree relative with diabetes, having glucose show up in the urine early in pregnancy, being significantly overweight, and having a previous newborn weighing 9 pounds or greater at the time of birth.

Clinical Recommendations for Gestational Diabetes Screening

Some experts have shown that screening every woman for gestational diabetes should be undertaken, while the US Preventative Services Task Force indicates that there is no evidence that all women should be screened for the disorder.  In those women who have been screened and found to have gestational diabetes, treatment recommendations include following the blood sugars on a fasting basis as well as following the blood sugars 2 hours after eating.

After a woman has been screened for gestational diabetes and has been found to have the disorder, most experts recommend antenatal testing during the pregnancy, including measuring the amniotic fluid volumes, ultrasound testing, and non-stress testing during the pregnancy.  If the blood sugars remain elevated after adequate lifestyle management, the pregnant woman should have some sort of medication treatment during the pregnancy.

In addition, those women who have been found to have gestational diabetes have a greater chance of having type 2 diabetes later in life so that, after the pregnancy is over, these women should be screened for type 2 diabetes for the rest of their lives.

The Screening Test for Gestational Diabetes

Gestational Diabetes Diagnosis and TestsThe current recommendation for gestational diabetes includes a one-hour glucose challenge test.  This involves giving the woman a 50-gram load of glucose at about 24-28 weeks’ gestation by having the woman drink a sugary beverage on a non-fasting basis.  After the glucose beverage has been given, the blood sugar is measured one hour after drinking the beverage.

If the blood sugar level is 130 mg/dL or more during this test, it is considered a positive test, however this does not prove that the woman has gestational diabetes.  For this, a 3-hour glucose tolerance test is given to clinch the diagnosis of gestational diabetes.   A fasting blood glucose level is another test for gestational diabetes but it is not considered specific enough to make the diagnosis so it is rarely used to make the diagnosis of the disorder.

As mentioned, the 50-gram oral glucose tolerance test is simply a screening test and does not mean the woman definitely has gestational diabetes.  If this is positive, the woman needs to have the 100-gram glucose tolerance test.  This involves giving the pregnant woman 100 grams of oral glucose solution after checking a fasting blood glucose level and then checking the blood sugars at one half hour, one hour, two hours, and three hours after giving the glucose solution.

In the 3-hour glucose tolerance test, a fasting blood sugar of 95 mg/dL or greater is considered a positive test for gestational diabetes.  A 1-hour level glucose level of 180 mg/dL or more is also considered a positive test.  A two-hour level of 155 mg/dL or more is considered positive for gestational diabetes and a three-hour level of 140 mg/dL or more is also an indication of gestational diabetes.

The 50-gram load glucose tolerance test is the screening test recommended in the US; however, in other parts of the world, the pregnant woman is given a 75-gram glucose load, which serves as a screening test as well as a diagnostic test for gestational diabetes.  In this way, only one test is required to make the diagnosis of gestational diabetes rather than two separate tests as is done in the US.


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