What is gestational diabetes mellitus (GDM)?

Gestational diabetes mellitus (GDM) is a condition in which the glucose level is elevated and other diabetic symptoms appear during pregnancy in a woman who has not previously been diagnosed with diabetes. All diabetic symptoms disappear following delivery.

Unlike type 1 diabetes, gestational diabetes is not caused by a lack of insulin, but by blocking effects of other hormones on the insulin that is produced, a condition referred to as insulin resistance.

Approximately 3 percent to 8 percent of all pregnant women in the United States are diagnosed with gestational diabetes.

What causes GDM?

Although the cause of GDM is not known, there are some theories as to why the condition occurs.

The placenta supplies a growing fetus with nutrients and water, as well as produces a variety of hormones to maintain the pregnancy. Some of these hormones (estrogen, cortisol, and human placental lactogen) can have a blocking effect on insulin. This is called contra-insulin effect, which usually begins about 20 to 24 weeks into the pregnancy.

As the placenta grows, more of these hormones are produced, and insulin resistance becomes greater. Normally, the pancreas is able to make additional insulin to overcome insulin resistance, but when the production of insulin is not enough to overcome the effect of the placental hormones, gestational diabetes results.

What are the risks factors associated with GDM?

Although any woman can develop GDM during pregnancy, some of the factors that may increase the risk include the following:

  • Overweight or obesity

  • Family history of diabetes

  • Having given birth previously to a very large infant, a still birth, or a child with a birth defect

  • Age (women who are older than 25 are at a greater risk for developing gestational diabetes than younger women)

  • Race (women who are African-American, American Indian, Asian American, Hispanic/Latino, or Pacific Islander have a higher risk)

  • Prediabetes

Although increased glucose in the urine is often included in the list of risk factors, it is not believed to be a reliable indicator for GDM.

How is GDM diagnosed?

New Standards of Medical Care in Diabetes-2011 from the American Diabetes Association recommend screening for undiagnosed type 2 diabetes at the first prenatal visit in women with diabetes risk factors. In pregnant women not known to have diabetes, GDM testing should be performed at 24 to 28 weeks of gestation.

In addition, women with diagnosed GDM should be screened for persistent diabetes 6-12 weeks postpartum. Women with a history of GDM are now recommended to have life-long screening for the development of diabetes or prediabetes at least every three years.

What is the treatment for GDM?

Specific treatment for gestational diabetes will be determined by your physician based on:

  • Your age, overall health, and medical history

  • Extent of the disease

  • Your tolerance for specific medications, procedures, or therapies

  • Expectations for the course of the disease

  • Your opinion or preference

Treatment for gestational diabetes focuses on keeping blood glucose levels in the normal range. Treatment may include:

  • Special diet

  • Exercise

  • Daily blood glucose monitoring

  • Insulin injections

Possible complications for the baby

Unlike type 1 diabetes, gestational diabetes generally does not cause birth defects. Birth defects usually originate sometime during the first trimester (before the 13th week) of pregnancy. But, the insulin resistance from the contra-insulin hormones produced by the placenta does not usually occur until approximately the 24th week. Women with gestational diabetes mellitus generally have normal blood sugar levels during the critical first trimester.

The complications of GDM are usually manageable and preventable. The key to prevention is careful control of blood sugar levels just as soon as the diagnosis of diabetes is made.

Infants of mothers with gestational diabetes are vulnerable to several chemical imbalances, such as low serum calcium and low serum magnesium levels, but, in general, there are two major problems of gestational diabetes: macrosomia and hypoglycemia.

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If you are pregnant or have a heavy menstrual period, you may need an iron supplement. A 2007 study in the American Journal of Clinical Nutrition found that women moderately deficient in iron had difficulties with memory and learning, but that an iron supplement resolved the problems. Pregnancy and heavy periods are two causes of iron deficiency.