What is Gestational Diabetes?


What is Gestational Diabetes Mellitus (GDM)?

Gestational diabetes is a form of diabetes that causes high blood glucose during pregnancy. As rates of type 2 diabetes increase worldwide, so do rates of gestational diabetes. About 1 in 10 pregnant women is diagnosed with gestational diabetes. GDM is commonly diagnosed as high blood glucose starting between 24 and 28 weeks of pregnancy. Occasionally it is diagnosed earlier in pregnancy, which may indicate high blood glucose prior to pregnancy. 

What causes GDM?

In all pregnancies, hormones secreted by the placenta interfere with the body’s use of insulin causing what’s called insulin resistance. If insulin production is not high enough to counter the insulin resistance, blood glucose rises.

What happens when blood glucose is high in pregnancy?

High blood glucose is known to cause adverse outcomes in pregnancy. In the first trimester, high blood glucose can cause pregnancy loss or malformations in the baby. Later in pregnancy, as a mother’s elevated blood glucose crosses the placenta, it will cause the baby to produce insulin in response. Excessive insulin leads to excessive growth of the baby. This can cause issues during labor and delivery, increasing cesarean section rate as well as neonatal hypoglycemia (baby’s low blood glucose at birth). In addition, babies who have grown excessively are at risk for childhood obesity and type 2 diabetes.

What are the signs of GDM?

Some women may experience thirst, frequent urination or exhaustion when they have high blood glucose levels. However, all of these symptoms are common in pregnancy. Therefore symptoms are not used to diagnose or determine testing for GDM.

How is GDM diagnosed?

Gestational diabetes is diagnosed through either the “Glucose Challenge Test” or one of two “Glucose Tolerance Tests.” Different healthcare providers use different tests depending on their practice and the results of each test. In addition, many also order an A1c test to determine how high blood glucose levels have been over the previous three months.

Who should be tested for GDM?

All women should be tested for gestational diabetes no later than 24-28 weeks. Women who are at higher risk for gestational diabetes should be tested earlier in pregnancy.

What makes a woman higher risk for GDM?

  • GDM in a previous pregnancy
  • History of prediabetes (A1c 5.7-6.4)
  • Elevated Body Mass Index (BMI)
  • A previous baby larger than 4000 gm (about 9 pounds)
  • History of Polycystic Ovarian Syndrome (PCOS)
  • History of hypertension or metabolic disease
  • Advanced maternal age (>35)
  • Lack of physical activity
  • High-risk ethnicity (African American, Latina, Asian American, Native American, Pacific Islander)
  • Family history of diabetes in a first-degree relative

Can GDM be prevented?

There are no evidence-based recommendations specifically for preventing GDM. However, getting preconception care to check for preexisting diabetes is extremely important. Also starting pregnancy with a normal BMI and a healthy lifestyle including both diet and exercise are important for overall health in pregnancy.

WRITTEN BY Jessica Lynn, MSN, CNM, CDE , POSTED 12/13/19, UPDATED 10/17/22

Jessica Lynn, MSN, CNM, CDE is a nurse midwife and perinatal diabetes educator in New York City. Her passion is helping women with diabetes have healthy pregnancies and births on their own terms. You can find her at diabetesmidwife.com