Gestational diabetes is a condition characterized by high blood glucose (sugar) levels that is first recognized during pregnancy. The condition occurs in approximately 4% of all pregnancies.

What Causes Gestational Diabetes?

Almost all women have some degree of impaired glucose intolerance during pregnancy as a result of hormonal changes that occur during pregnancy. That means that their blood sugar may be higher than normal, but not high enough to have diabetes. During the later part of pregnancy (the third trimester), these hormonal changes place pregnant woman at risk for gestational diabetes.

During pregnancy, increased levels of certain hormones made in the placenta (the organ that connects the baby by the umbilical cord to the uterus) help shift nutrients from the mother to the developing fetus. Other hormones are produced by the placenta to help prevent the mother from developing low blood sugar. They work by stopping the actions of insulin.

Over the course of the pregnancy, these hormones lead to progressive impaired glucose intolerance (higher blood glucose levels). To try to decrease the glucose levels, the body makes more insulin to shuttle glucose into cells.

Usually the mother's pancreas is able to produce more insulin (about three times the normal amount) to overcome the effect of the pregnancy hormones on glucose levels. If, however, the pancreas cannot produce enough insulin to overcome the effect of the increased hormones during pregnancy, glucose levels will rise, resulting in gestational diabetes.

What Are the Complications of Gestational Diabetes?

Diabetes in a pregnant woman can affect the developing baby throughout the pregnancy. In early pregnancy, maternal diabetes can result in birth defects and an increased rate of miscarriage. Many of the birth defects that occur affect major organs such as the brain and heart.

During the second and third trimester, maternal diabetes can lead to over-nutrition and excess growth of the baby. Having a large baby increases risks during labor and delivery. For example, large babies often require caesarean deliveries and if he or she is delivered vaginally, they are at increased risk for trauma to their shoulder.

In addition, when fetal over-nutrition occurs and hyperinsulinemia results, the baby's blood glucose can drop very low after birth, since it won't be receiving the high blood glucose from the mother.

However, with proper treatment, you can deliver a healthy baby despite having gestational diabetes.

Who Is at Risk for Gestational Diabetes?

The following factors increase the risk of developing diabetes during pregnancy:

Being overweight prior to becoming pregnant (if you are 20% or more over your ideal body weight).
Being a member of a high risk ethnic group (Hispanic, black, Native American, or Asian).
Having glucose in your urine.
Impaired glucose tolerance or impaired fasting glucose (blood glucose levels are high, but not high enough to be diabetes).
Family history of diabetes (if your parents or siblings have diabetes).
Previously giving birth to a baby over 9 pounds.
Previously giving birth to a stillborn baby.
Having gestational diabetes with a previous pregnancy.
Having too much amniotic fluid (a condition called polyhydramnios).

Many women who develop gestational diabetes have no known risk factors.