Gestational Diabetes Mellitus (GDM) Overview

GDM, also called gestational diabetes, is a form of diabetes that develops during pregnancy. It affects up to about 9% of U.S. pregnancies and is typically diagnosed around the 24th to 28th week of pregnancy.^{1 - 3} GDM develops when placental hormones interfere with insulin's ability to move glucose into cells, causing insulin resistance.^{4 - 7} While all pregnant women experience some level of insulin resistance, GDM occurs when the body cannot produce enough insulin to maintain normal glucose levels. It is characterized by hyperglycemia and may cause increased fatigue or shakiness, frequent urination, or swelling in the hands or face.^{4 , 5 , 8 , 9} However, most women with GDM have no symptoms or have only mild symptoms, so routine screening is essential.

Women who develop GDM face increased risks of pregnancy complications such as hypertension, pre-eclampsia, and cesarean delivery.^{2 - 4 , 6 , 7 , 9 - 12} Risks to the baby include preterm birth, stillbirth, macrosomia, hyperbilirubinemia, birth defects, neonatal hypoglycemia, respiratory problems, and a higher risk of obesity and type 2 diabetes later in life.^{2 , 4 - 7 , 9 - 13} Although hyperglycemia usually resolves after delivery, GDM requires careful management to protect the health of the mother and child. Additionally, GDM poses long-term health implications for the mother; about 50% to 60% of women with GDM go on to develop type 2 diabetes in subsequent years, making postpartum blood glucose monitoring essential.^{4 , 6 , 9 - 11} Women with a recent history of GDM should be screened at 4 to 12 weeks postpartum using a fasting 75-g oral glucose tolerance test and clinically appropriate nonpregnancy diagnostic criteria, with retesting every 1 to 3 years thereafter.¹¹ GDM may also recur in future pregnancies, underscoring the persistent metabolic vulnerability in women who have had the condition.

Risk factors for GDM include being overweight or having obesity, having a family history of type 2 diabetes, being older than 25, having had GDM in a previous pregnancy, and having polycystic ovary syndrome.^{1 , 3 - 5 , 7 , 9 , 10} GDM is also more common in women who are Black or of Hispanic/Latino, Native American, Alaska Native, Native Hawaiian, Asian, or Pacific Islander backgrounds.^{1 - 5 , 7 , 9 , 10}

Diagnosis of GDM typically involves blood glucose screening between 24 and 28 weeks of pregnancy using tests such as the glucose challenge test and oral glucose tolerance test.^{1 - 5 , 7 , 9 - 11 , 13} Treatment focuses on maintaining healthy blood glucose levels through diet, exercise, and—if necessary—administering insulin when lifestyle interventions aren't sufficient.^{1 , 3 - 7 , 9 - 11 , 13 , 14} Other therapeutic options include metformin and glyburide, but the American Diabetes Association states that these medications should not be used as first-line agents because both of them cross the placenta.¹¹ Dietary recommendations include consuming whole fruits and vegetables; incorporating moderate amounts of whole grains, starchy vegetables, lean protein, and healthy fats; and limiting foods that contain added sugars.^{11 , 15} Women are also advised to monitor their blood glucose at home, follow individualized nutrition planning, and engage in moderate physical activity.^{5 , 6} Target blood glucose levels for women with GDM include a fasting level below 95 mg/dL, a 1-hour postprandial level below 140 mg/dL, and a 2-hour postprandial level below 120 mg/dL.^{9 , 11}

Current research is aimed at identifying the genetic factors that influence the development and recurrence of GDM, evaluating potential diagnostic criteria before 20 weeks gestation, and identifying biochemical markers that are related to glucose intolerance and fetal outcomes.^{16 , 17} Further research is also needed to refine the diagnostic criteria for GDM; some researchers are exploring the use of a precision medicine approach that recognizes GDM as a heterogeneous condition that might require distinct diagnostic strategies.^{13 , 16 , 18} In addition, studies are needed to refine dietary inventions, including establishing an optimal carbohydrate threshold; establish optimal monitoring strategies during pregnancy and the postpartum period, including the application of continuous glucose monitoring to manage GDM during pregnancy; and evaluate the comparative effectiveness and safety of insulin, metformin, and glyburide with respect to both perinatal and long-term maternal and child outcomes.^{13 , 16 , 18 - 20}

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) is funding the Glycemic Observation and Metabolic Outcomes in Mothers and Offspring (GO MOMs) study to examine maternal glycemia during pregnancy and evaluate how glucose levels relate to perinatal outcomes and traditional third-trimester GDM screening. Its purpose is to develop criteria using continuous glucose monitoring technology and glucose tolerance testing conducted early in gestation to predict adverse maternal and fetal pregnancy outcomes. The GO MOMs as above will provide the foundational evidence needed to inform future strategies for screening, diagnosing, and treating hyperglycemia in pregnancy.

The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) also supports research initiatives related to GDM. The overarching goal of these efforts is to understand the epidemiology and etiology of GDM in order to develop effective and targeted intervention strategies to prevent this pregnancy complication.