According to the CDC, the reported rates of gestational diabetes mellitus (GDM) range from 2% to 10% of all pregnancies. Immediately after pregnancy, 5% to 10% of women with GDM are found to have diabetes. In the United States, women who have had GDM have more than a 60% chance of developing diabetes in the next 10 to 20 years. Poorly controlled diabetes carries more serious risks. These risks include large size, preeclampsia, pre-term delivery, stillbirth and respiratory distress, and other problems for the newborn baby. However, optimizing blood glucose levels before and during pregnancy may reduce these risks.
“GDM used to be defined as any degree of glucose intolerance with onset or first recognition during pregnancy, whether or not the condition persisted after pregnancy, and with the possibility that unrecognized glucose intolerance may have predated or begun concomitantly with pregnancy,” explains Boyd E. Metzger, MD. “This definition led to the development of a uniform strategy for detecting and classifying GDM. The ongoing epidemic of obesity and diabetes, however, has led to more cases of type 2 diabetes in women of childbearing age. As a result, the number of pregnant women with undiagnosed type 2 diabetes has increased. As such, efforts should be made to screen women for diabetes at their initial prenatal visit using standard diagnostic criteria if they have risk factors for diabetes [Table 1]. When diabetes is found at this visit, women should receive a diagnosis of overt diabetes rather than GDM and treated accordingly.”
Published research has documented that GDM carries risks for both mothers and neonates. In the American Diabetes Association’s Standards of Medical Care in Diabetes—2011, the Association officially adopted new diagnostic criteria for GDM based largely on findings from the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study. This was a large-scale multinational epidemiologic study involving about 25,000 pregnant women. It demonstrated that the risk of adverse maternal, fetal, and neonatal outcomes continuously increased as a function of maternal glycemia at 24 to 28 weeks, even within glycemic ranges previously considered normal for pregnancy. For the complications examined in the study, there was no glycemic threshold for risk.
“Efforts should be made to screen women for diabetes at their initial prenatal visit using standard diagnostic criteria if they have risk factors for diabetes.”
“The objective of the HAPO study was to clarify the associations of levels of maternal glucose lower than those diagnostic of diabetes with perinatal outcome,” says Dr. Metzger. “There were continuous graded relationships between higher maternal glucose and increasing frequency of the primary outcomes. These associations did not differ among centers, so the results are considered applicable to all centers and can be used globally to develop outcome-based criteria for classifying glucose metabolism in pregnancy.”
Results from the HAPO study have led to careful reconsideration of the diagnostic criteria for GDM. The International Association of Diabetes and Pregnancy Study Groups, an international consensus group with representatives from multiple obstetrical and diabetes organizations, including the American Diabetes Association, developed revised recommendations for diagnosing GDM (Table 2). The group recommended that all women not known to have diabetes undergo a 75-gram oral glucose tolerance test (OGTT) at 24-to-28 weeks of gestation. Additionally, diagnostic cut points were established for the fasting, 1-hour, and 2-hour plasma glucose measurements.
“The new criteria for diagnosing GDM will significantly increase the prevalence of the disease,” says Dr. Metzger. “This is primarily because only one abnormal value—not two—is sufficient to make a diagnosis.” The American Diabetes Association noted in its Standards of Medical Care in Diabetes—2011 that the diagnostic criteria changes were made in the context of worrisome increases in obesity and diabetes rates with the intent of optimizing gestational outcomes for women and their babies. Two randomized controlled treatment trials of “mild” GDM have shown benefit of treatment and the treatment primarily involved lifestyle changes and medical nutritional therapy. However, Dr. Metzger adds that there are few data regarding therapeutic interventions in women who will now be diagnosed with GDM based on the new diagnostic criteria. “We’ll need to design studies to determine the optimal intensity of monitoring and treatment of women with GDM diagnosed by the new criteria,” he says.
Tried and True Screening Practices
As with previous recommendations from the American Diabetes Association, clinicians are urged to screen women with a history of GDM for diabetes 6 to 12 weeks postpartum using non-pregnant OGTT criteria because some cases may represent preexisting undiagnosed diabetes. “Women with a history of GDM have a greatly increased subsequent risk for diabetes and should be followed up with subsequent screening for the development of diabetes or prediabetes,” adds Dr. Metzger. “Women with a history of GDM should have lifelong screening for the development of diabetes or prediabetes at least every 3 years.”
American Diabetes Association. Standards of Medical Care in Diabetes—2011. Diabetes Care.2011;34:S11-S61. Available at: http://care.diabetesjournals.org/content/34/Supplement_1/S11.full.
AHRQ. Gestational diabetes: caring for women during and after pregnancy. Available at:http://effectivehealthcare.ahrq.gov/ehc/products/107/163/2009_0804GDM_Clinician_final.pdf.
Lawrence JM, Contreras R, Chen W, Sacks DA. Trends in the prevalence of preexisting diabetes and gestational diabetes mellitus among a racially/ethnically diverse population of pregnant women, 1999–2005.Diabetes Care. 2008;31:899-904.
HAPO Study Cooperative Research Group, Metzger BE, Lowe LP, Dyer AR, et al. Hyperglycemia and adverse pregnancy outcomes. N Engl J Med. 2008;358:1991-2002.