Joslin Diabetes Center

About Diabetes

Gestational Diabetes

What is Gestational Diabetes?

Gestational diabetes 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 to 5 percent of all pregnant women in the United States are diagnosed with gestational diabetes.

What Causes Gestational Diabetes?

Although the cause of gestational diabetes 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 Gestational Diabetes?

Although any woman might develop gestational diabetes during pregnancy, some of the factors that may increase risk are:

obesity
family history of diabetes
having given birth previously to a very large infant, a still birth, or a child with a birth defect
having too much amniotic fluid (polyhydramnios)
women who are older than 25 are at greater risk than younger women

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 gestational diabetes.

How is Gestational Diabetes Diagnosed?

Gestational diabetes is diagnosed with a glucose screening test, which involves drinking a glucose drink followed by measurement of glucose levels after a one-hour interval.

If this test shows a blood sugar level of greater than 140 mg/dl, another test will be performed after a few days of following a special diet. The second test also involves drinking a glucose drink, and results are measured at three-hour intervals.

If results of the second test are in the abnormal range, gestational diabetes is diagnosed.

Treatment for Gestational Diabetes:

Specific treatment will be determined by your physician(s) 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 generally have normal blood sugar levels during the critical first trimester.

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

Macrosomia - refers to a baby that is considerably larger than normal. All of the nutrients the fetus receives come directly from the mother's blood. If the maternal blood has too much glucose, the pancreas of the fetus senses the high glucose levels and produces more insulin in an attempt to use this glucose. The fetus converts the extra glucose to fat. Even when the mother has gestational diabetes, the fetus is able to produce all the insulin it needs. The combination of high blood glucose levels from the mother and high insulin levels in the fetus results in large deposits of fat which causes the fetus to grow excessively large.
Hypoglycemia - refers to low blood sugar in the baby immediately after delivery. This problem occurs if the mother's blood sugar levels have been consistently high causing the fetus to have a high level of insulin in its circulation. After delivery, the baby continues to have a high insulin level, but it no longer has the high level of sugar from its mother, resulting in the newborn's blood sugar level becoming very low. The baby's blood sugar level is checked after birth, and if the level is too low, it may be necessary to give the baby glucose intravenously.

Our Services:

Learn more about the services offered at The Joslin Diabetes Center at University of Maryland:

This page was last updated on: August 20, 2007.

For appointments or information, call 1-888-JOSLIN8 (1-888-567-5468).