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An expert commentary on ACOG Practice Bulletin No. 137.
Committee on Practice Bulletins-Obstetrics
ACOG Practice Bulletin 137: Gestational Diabetes Mellitus, August 2013 (Replaces Practice Bulletin Number 30, September 2001, Committee Opinion Number 435, June 2009, and Committee Opinion Number 504, September 2011).
Obstet Gynecol. 2013;122:406-16. Full text of ACOG Practice Bulletins is available to ACOG members at http://www.acog.org/Resources_And_Publications/Practice_Bulletins/Committee_on_Practice _Bulletins_--_Obstetrics/Gestational_Diabetes_Mellitus.
Gestational diabetes mellitus (GDM) is one of the most common medical complications of pregnancy. Debate continues to surround both the diagnosis and treatment of GDM despite several recent large-scale studies addressing these issues. The purpose of this document is to 1) provide a brief overview of the understanding of GDM, 2) provide management guidelines that have been validated by appropriately conducted clinical research, and 3) identify gaps in current knowledge toward which future research can be directed.
Used with permission. Copyright the American College of Obstetricians and Gynecologists.
By Haywood L. Brown, MD
Dr. Brown is Roy T. Parker Professor and Chair, Department of Obstetrics and Gynecology, Division of Maternal Fetal Medicine, Duke Medicine, Durham, NC. He is also a member of the Contemporary OB/GYN Editorial Board.
Practice Bulletin 137 on gestational diabetes mellitus provides a rationale for current screening guidelines for a pregnancy population in which prevalence of obesity and Type 2 diabetes has increased over the past several decades.
Review of the bulletin underscores several questions pertinent to diagnosis and management, which are reflected by and addressed similarly in the evidence-based recommendations in the document.1
Obviously, the prevalence of gestational diabetes mellitus (GDM) in the population varies in proportion to the prevalence of Type 2 diabetes. However, determination of the prevalence of GDM and identification of those at higher risk of developing this common medical complication of pregnancy must begin with an appreciation of the cost, benefits, and goals of screening.
Once the diagnosis of GDM is confirmed, the factors to be considered are the subsequent excess costs derived from more rigorous antenatal follow-up, including additional testing and monitoring of both mother and fetus, and ultimately clinical decision-making around intrapartum management to prevent perinatal morbidity and mortality.
There is little doubt that women with GDM are at higher risk of adverse pregnancy outcomes. These include large-for-gestational-age (LGA) birth weight/macrosomia, shoulder dystocia, stillbirth, and neonatal morbidities such as hypoglycemia, respiratory distress, and neonatal intensive care admission, especially when the diabetes is poorly controlled.
Beyond reduction of perinatal morbidity and mortality, another important goal of GDM screening is identification of those at risk of developing Type 2 diabetes, especially those in high-risk ethnic groups. For the woman who has GDM, counseling and implementation of interconception lifestyle modifications will benefit subsequent pregnancies and should have both short- and long-term health benefits related to development of maternal morbidities and mortality.
For decades obstetricians have debated criteria for diagnosis of GDM and whether to use the O’Sullivan and Mahan or Carpenter and Coustan cutoff thresholds. Using the lower threshold for abnormal values as proposed by the Carpenter and Coustan criteria increases the number of women with the diagnosis.
Another debate has been the employment of selective versus universal screening. ACOG has adopted universal screening for GDM because the majority of women in antenatal care have at least one traditional risk factor. Over half of the women who make up the US obstetric population-and particularly women of Latina or African descent-are overweight or obese and/or have a first-degree relative with diabetes.
In 2010, the International Association of Diabetes and Pregnancy (IADP) Study recommended universal screening with a 75-g 2-hour test at 24 to 32 weeks and diagnosis of GDM established with a single abnormal value, and acknowledged that testing with this strategy would increase the diagnosis of GDM.2 Obviously increasing the number of women with the diagnosis increases the cost of care. The 2013 National Institutes of Health Consensus Conference did not recommend adoption of the IADP Study group recommendation.3
Therefore, ACOG continues to recommend the 2-step diagnostic approach to screening using a cutoff for an abnormal 1-hour screen of 135–140 mg/dL and 2 abnormal values on the 3-hour oral glucose tolerance test that includes a fasting value. In our practice, we use 140 mg/dL for the 1-hour screen, as suggested in the ACOG Practice Bulletin, based on community prevalence rates of GDM.
More than half of the pregnant population in the United States meet the criteria for early screening for diabetes including women with BMI ≥ 30 and strong family history. These women are subjected to a second test between 26 and 30 weeks if the initial screen is normal, which is very likely in women who are at the lower limit for obesity (BMI 30–35). Perhaps this practice should be reevaluated, or at least BMI criteria for early testing for diabetes revised.
As important to an accurate diagnosis is management of GDM. The favored approach includes counseling on appropriate weight gain, exercise, and diet and/or pharmacologic treatment to achieve optimal control.
Split-dose insulin therapy with a moderate or long-acting insulin and shorter-acting insulin has been standard pharmacologic treatment for GDM. More recently, oral hypoglycemic agents have been used. For insulin and oral hypoglycemic agents to be most effective in treating GDM, patients should monitor fasting and postprandial blood sugars several times a day, and medication should be adjusted accordingly to achieve euglycemia.
Most patients with GDM favor oral hypoglycemic agents in their management regimen. Randomized trials show that glyburide and insulin are equally effective in achieving glycemic control. Other trials comparing glyburide to metformin suggest that glyburide is more effective than metformin because treatment with metformin is more likely to require the addition of insulin to achieve glycemic control. Both medications have been shown to have favorable safety profiles and the risk of neonatal hypoglycemia is of concern whether an oral agent or insulin is used to achieve maternal euglycemia.
In the Australian Carbohydrate Intolerance Study in Pregnant Women, women with GDM were randomized to dietary advice, blood glucose monitoring, and insulin therapy as needed in the intervention group versus routine care. Treatment was associated with a significant reduction in composite serious complications including LGA, shoulder dystocia, and perinatal death.4
In 2009, investigators from the Eunice Kennedy Shriver National Institute of Child Health and Human Development and Maternal-Fetal Medicine Units Network reported on randomization of 958 women to treatment for GDM versus a control group that received usual prenatal care. This control group had an abnormal 50-g 1-hour screen but a normal 3-hour test. There was no difference in the frequency of primary composite outcome that included perinatal death but there was a similarly lower frequency of various birth outcomes, including LGA infants, in women who were treated.5
The confounder in most trials of pharmacologic agents for treatment of GDM, however, is the adherence (or lack thereof) to an appropriate diet. What is the importance of diet in management of GDM? This factor is often forgotten in modern management of GDM.
Nutrition counseling throughout pregnancy is an essential adjunct to pharmacologic treatment. Adherence to a diet with an appropriate intake of carbohydrates, protein, and fat, along with control of weight gain, leads to less need for medication adjustment to treat abnormal blood sugars and achieve euglycemia in pregnant women, as in most nonpregnant patients with diabetes.
In most women with GDM diagnosed by 2 abnormal values not including an abnormal fasting value on the 3-hour panel, diet and exercise therapy alone can be used to manage the condition and bring fasting and postprandial glucose levels into an acceptable euglycemic range.
What about mode and timing of delivery, especially in the case of macrosomia or poor control? Ultrasound estimation of fetal weight is not without error but prevention of morbidity and birth trauma can be decreased by adherence to the guidelines of offering a cesarean delivery to pregnant diabetics who have an estimated fetal weight greater than 4500 g.
Furthermore, clinicians must appreciate that in women with good glycemic control, delivery should not occur before 39 weeks unless the pregnancy is further complicated by other factors such as preeclampsia. The temptation to expedite delivery prior to 39 weeks in patients whose condition is well controlled on diet or diet plus medical therapy increases the risk of cesarean delivery in cases of induction with an unfavorable cervix and of neonatal morbidity.
Whether GDM is overdiagnosed or underdiagnosed, the point of screening and diagnosis is to decrease perinatal and obstetric morbidity.
Moreover, another essential focus must be to take advantage of the opportunity to implement interventions aimed at the mother’s long-term health. This begins with the postpartum glucose screening and a discussion aimed at decreasing the risk of recurrence of GDM and development of “familial” diabetes later in adult life. For these reasons, but mostly the latter, this obstetrician leans toward overdiagnosis of GDM.
1. American College of Obstetricians and Gynecologists. Gestational Diabetes Mellitus. Practice Bulletin 137, August 2013.
2. Mertzger BE, Gabbe SG, Persson B, et al. International association of diabetes and pregnancy study group recommendation on the diagnosis and classification of hyperglycemia in pregnancy. International Association of Diabetes and Pregnancy Study Groups Consensus Panel. Diabetes Care. 2010;33:676–682.
3. VanDorsten JP, Dodson WE, Espeland MA, et al. Diagnosing gestational diabetes mellitus. National Institutes of health Consensus State Sci Statements 2013;29(1):1–30.
4. Crowther CA, Hiller JE, Moss JR, McPhee AJ, Jeffries WS, Robinson JS. Effect of treatment of gestational diabetes mellitus on pregnancy outcomes. Australian Carohydrate Intollerance Study in Pregnancy Women (ACHOIS ) Trial Group. N Engl J Med. 2005;352-2477–2486.
5. Landon MB, Spong CY, Thom E, et al. A multicenter, randomized trial of treatment for mild gestational diabetes. Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. N Engl J Med. 2009;361:1339–1348.