Gestational Diabetes

What is Gestational Diabetes?
Gestational diabetes is diabetes mellitus that develops in women for the 1st time during pregnancy.  Some women diagnosed with gestational diabetes during pregnancy may actually have had mild, undiagnosed diabetes mellitus before pregnancy.

What Causes Gestational Diabetes?
Gestational diabetes is caused by the way a woman’s body responds to insulin during pregnancy.  Pregnancy is characterized by increasing insulin resistance as the pregnancy progresses.  This change is designed to increase the mother’s blood glucose level and make more nutrients available to the baby.  Typically, the mother’s body produces additional insulin to keep blood glucose levels normal.  However, in a small percentage of women, this additional insulin production is not sufficient to keep blood glucose levels in a normal range, and they develop gestational diabetes.

What are Risk Factors for Gestational Diabetes?

  • Obesity with Body Mass Index (BMI) > 30
  • History of gestational diabetes with a previous pregnancy
  • History of a very large baby ≥ 9 pounds
  • Advanced maternal age  ≥ 35
  • Family history of diabetes
  • African American, American Indian, Asian American, Hispanic, Latina or Pacific Islander race

What Tests are Used to Screen for Gestational Diabetes?
The American College of Obstetrics and Gynecology recommends that all pregnant women be screened for gestational diabetes. 

The 1 Hour Glucose Tolerance Test (GTT or “O’Sullivan”) is the first-line screening test to evaluate for gestational diabetes.  This test is performed on every patient between 24 and 28 weeks of pregnancy.  Some patients who are at especially high risk for developing gestational diabetes will also be advised to perform an “Early O’Sullivan” at 14-16 weeks of pregnancy.  Even if you “pass” the Early O’Sullivan test, you will still need to repeat the test between 26 and 28 weeks of pregnancy.

If the O’Sullivan test result is abnormal, an additional fasting 3 Hour Glucose Tolerance Test is ordered.  During this 3 Hour GTT, a fasting blood glucose level is checked, and then, after drinking a 100g Glucola solution, blood glucose levels are monitored hourly for 3 hours .  Two abnormal values confirm a diagnosis of gestational diabetes.

1 Hour Glucose Tolerance Test Instructions
3 Hour Glucose Tolerance Test Instructions
Jelly Bean Glucose Tolerance Test Instructions

How Can Gestational Diabetes Affect My Pregnancy?
Gestational diabetes increases the risks of having a very large baby, requiring a c-section for delivery, or having a vaginal delivery complicated by a shoulder dystocia.  Gestational hypertension and preeclampsia are also more common in women with gestational diabetes.

Babies born to mothers with gestational diabetes are at increased risk for low blood glucose levels (hypoglycemia) immediately after delivery, respiratory difficulties and jaundice.   If blood sugar is very poorly controlled during pregnancy, there is an increased risk of stillbirth.  Optimal blood glucose control reduces these risks.

What is the Treatment for Gestational Diabetes?
If you are diagnosed with gestational diabetes, you will be immediately referred to a Diabetic Educator to review diet recommendations and blood sugar testing.  Gestational diabetes requires close monitoring of blood sugar levels with an instrument called a “glucometer”.  These levels are typically checked fasting each morning, and then 2 hours after each meal.  It is essential to record blood glucose levels in a log every day and to bring this log with you to every OB appointment.  An accurate blood sugar log is essential for your provider to evaluate your glucose control.  Blood glucose levels can usually be controlled with diet modification and exercise.  Goal glucose levels are:

  • Fasting glucose level ≤ 95
  • 2-hour post-prandial glucose level ≤ 120
  • 1-hour post-prandial glucose level ≤ 140

If your blood glucose levels are consistently above the goal ranges, you may require oral medication or injectable insulin.  Patients who require medication to control their glucose levels undergo more intensive fetal monitoring with ultrasounds approximately every 4 weeks to measure fetal growth and twice-weekly non-stress tests (NSTs) beginning at 32 weeks gestation.  In most cases of medication-requiring gestational diabetes, we recommend delivery at 39 weeks gestation.

What are the Long-Term Effects of Gestational Diabetes?
Women with gestational diabetes are at increased risk of developing diabetes in the future.  Consequently, all women with gestational diabetes should have a test for diabetes performed at 6-12 weeks post partum.  These women will also require routine testing for diabetes at least every 3 years.

Children born to mothers with gestational diabetes are also at increased risk of developing diabetes.

Koop Kam 2

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Durant Medical Center
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