Gestational diabetes mellitus (GDM) is defined as the state of carbohydrate (glucose) intolerance that has its onset or first recognition during late pregnancy and has many similarities to non-insulin dependent diabetes mellitus (NIDDM).
GDM presents in two forms. The terms “overt” and “gestational diabetes” are used to describe the type of GDM, and are based primarily on gestational age at diagnosis. Diagnosis of diabetes at 24 to 28 weeks of gestation is consistent with "gestational diabetes," while diagnosis at the first prenatal visit (in early pregnancy) is more consistent with "overt diabetes".1 Risk factors such as a previous history of gestational diabetes, previous delivery of a baby > 9 pounds, obesity with BMI > 30 kg/m2, glycosuria at the first prenatal visit, and first degree relatives with diabetes will likely predispose these women to GDM.1
Pregnant women with GDM have an increased incidence of preeclampsia, preterm labor, pyelonephritis, polyhydramnios, and cesarean delivery. The long-term complications include a higher risk of developing NIDDM and cardiovascular disease.2
In addition, there are many potential effects of GDM on the fetus. Short-term effects include a much larger birth weight (fetal macrosomia), shoulder dystocia, difficult or operative delivery, stillbirth, increased perinatal morbidity and mortality. Long-term effects include an increased incidence of childhood obesity, early adulthood type 2 diabetes mellitus, and impaired intellectual-motor impairment.3
Therefore, it is imperative for clinicians to diagnose and treat GDM in pregnant women as soon as possible to prevent perinatal complications and to identify patients who may benefit from early interventions such as improved nutrition, weight loss, and a regular exercise program to prevent development of NIDDM and associated complications later in life.4
The American College of Obstetricians and Gynecologists (ACOG) recommends screening pregnant patients with a 50 gram oral glucose tolerance test (OGTT) between 24-28 weeks’ gestation. Patients with plasma glucose levels > 135 mg/dL after the oral glucose load should be evaluated with a diagnostic 3-hour OGTT. The 3-hour OGTT is conducted with a 100 gram glucose load. Subsequent blood samples are taken at 1, 2, and 3 hours. Based on the Carpenter and Coustan criteria, abnormal values are > 95 for fasting, > 180 mg/dL for 1-hour glucose concentration, > 155 mg/dL for 2-hour, and > 140 mg/dL for 3-hour. Two or more abnormal values confirm the diagnosis of gestational diabetes. 1, 5
Patients with GDM should receive exercise advise from a physician and nutritional counseling by a registered dietitian upon diagnosis. The goals of exercise and medical nutritional therapy are to achieve normal plasma glucose levels, to prevent the buildup of ketones (ketosis), to provide adequate (but not excessive) weight gain based on maternal body mass index, and to contribute to fetal well-being. ACOG recommends the target glucose to be ≤ 95 mg/dL for fasting blood glucose, ≤ 140 mg/dL for one-hour postprandial glucose concentration, and ≤ 120 mg/dL for two-hour.2
However, when normal plasma glucose levels are not achieved with an appropriate diet and exercise within 1-2 weeks, use of subcutaneous insulin products such as Lispro, and selected oral products such as Glyburide are recommended to keep the glucose near the target goal.6,8
Mothers with GDM should be advised to have frequent blood glucose testing following pregnancy. Thirty-five percent of women with GDM will develop overt diabetes within 5 to 10 years after delivery. Therefore, a patient with a history of GDM will need a 2-hour 75 g OGTT six to twelve weeks postpartum to determine if diabetes has resolved in order to prevent developing future cardiovascular disease. Those with normal glucose tolerance should be reassessed every 3 years. Those with impaired glucose tolerance or impaired fasting glucose should be reevaluated annually. Most importantly, these patients should be encouraged to maintain an appropriate diet, normal weight, and exercise regularly.4
Lylla Ngo, M.D
Thomas Hale, Ph.D
Image by Neal McQ
(You may also be interested in: Breastfeeding May Reduce the Risk of Type 2 Diabetes)
1. Coustan D, Jovanovic L. Diabetes mellitus in pregnancy: Screening and diagnosis. UpToDate. 03/07/2014 ed.
2. Coustan D, Jovanovic L. Diabetes mellitus in pregnancy: Glycemic control and maternal prognosis. UpToDate. 07/28/2014 ed.
3. Riskin A, Garcia-Prats J. Infant of a diabetic mother. UpToDate. 05/12/2014 ed.
4. Decherney A, Nathan L, Laufer N, Roman A. Current diagnosis and treatment: Obstetrics and gynecology. Eleventh ed: Lange; 2013.
5. Jovanovic L. Patient information: Gestational diabetes mellitus (Beyond the Basics). UpToDate. 03/12/2014 ed
6. Gaughey A. Gestational diabetes mellitus: Obstetrical issues and management. UpToDate. 03/15/2014 ed.
7. Camelo Castillo W, Boggess K, Sturmer T, Brookhart MA, Benjamin DK, Jr., Jonsson Funk M. Trends in glyburide compared with insulin use for gestational diabetes treatment in the United States, 2000-2011. Obstetrics and gynecology. Jun 2014;123(6):1177-1184.
8. Deepaklal MC, Joseph K, Kurian R, Thakkar NA. Efficacy of insulin lispro in improving glycemic control in gestational diabetes. Indian journal of endocrinology and metabolism. Jul 2014;18(4):491-495.
9. Sreckovic I, Birner-Gruenberger R, Besenboeck C, et al. Gestational diabetes mellitus modulates neonatal high-density lipoprotein composition and its functional heterogeneity. Biochimica et biophysica acta. Aug 12 2014.