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Universal versus selective gestational diabetes screening: Application of 1997 American Diabetes Association recommendations
Universal versus selective gestational diabetes screening: Application of 1997 American Diabetes Association recommendations Diana R. Danilenko-Dixon, MD, Jo T. Van Winter, MD, Roger L. Nelson, MD, and Paul L. Ogburn, Jr, MD Rochester, Minnesota OBJECTIVE: We sought to evaluate the impact of the 1997 American Diabetes Association gestational diabetes mellitus screening guidelines applied to a universally screened population. STUDY DESIGN: A retrospective analysis of 18,504 women universally screened for gestational diabetes mellitus at Mayo Clinic, Rochester, between January 1, 1986, and December 31, 1997, was performed. Diabetic screening consisted of plasma glucose determination 1 hour after a 50-g oral glucose challenge. Diagnosis of gestational diabetes mellitus was based on National Diabetes Data Group criteria. RESULTS: Of 564 cases of gestational diabetes mellitus diagnosed during the study period, 17 (3.0%) would have been missed under the 1997 American Diabetes Association selective screening guidelines while exempting only 10% of this predominantly white population from screening. Screening only women ≥25 years old would have detected 90.4% of gestational diabetes mellitus cases, whereas the addition of the remaining 3 screening criteria combined would have detected only an additional 6.6% of cases. CONCLUSIONS: The proportion of patients with gestational diabetes mellitus that would remain undiagnosed under the 1997 American Diabetes Association screening guidelines would be relatively small in our population. However, implementation of these guidelines would decrease the number of screens by only 10% while adding significant complexity to the screening process. Youth appears to be the most significant protective factor for gestational diabetes mellitus in our population. (Am J Obstet Gynecol 1999;181:798-802.)
Key words: Gestational diabetes mellitus screening, American Diabetes Association recommendations
Gestational diabetes mellitus (GDM) is defined as “carbohydrate intolerance of variable severity, with onset or first recognition during pregnancy.”1 Its incidence is highly population-specific, but in general 3% to 5% of pregnant women in this country receive this diagnosis. GDM was initially described in 1964 by O’Sullivan and Mahan,2 with documentation of the association between results of an oral glucose tolerance test during pregnancy and the future development of type 2 diabetes. Subsequently, GDM was associated with stillbirth, macrosomia, shoulder dystocia, birth trauma, need for operative delivery, neonatal hypoglycemia, and other perinatal morbidities. Despite >30 years of research, lack of consensus remains regarding nearly every clinical aspect of GDM—
From the Departments of Obstetrics and Gynecology and Endocrinology, Mayo Clinic. Presented at the Nineteenth Annual Meeting of the Society for MaternalFetal Medicine, San Francisco, California, January 18-23, 1999. Reprint requests: Diana R. Danilenko-Dixon, MD, Maternal-Fetal Medicine, Mayo Clinic, 200 First St SW, Rochester, MN 55905. Copyright © 1999 by Mosby, Inc. 0002-9378/99 $8.00 + 0 6/6/100571
798
the need to screen, diagnostic criteria, treatment, and even the validity of GDM as a meaningful diagnosis.3 Traditionally, universal screening of all pregnant women for GDM had been endorsed by both the American Diabetes Association Position Statement and by the First, Second, and Third International Workshop-Conferences on GDM.4-7 Meanwhile, The American College of Obstetricians and Gynecologists (ACOG) 1986 Technical Bulletin recommended selective screening for GDM for women ≥30 years old or for younger women with clinical or historical risk factors, such as prior GDM, obesity, family history of diabetes, or a prior macrosomic, anomalous, or stillborn infant.8 The more recent 1994 ACOG Technical Bulletin on diabetes and pregnancy fell short of recommending universal GDM screening, stating, “There are no data to support the benefit of screening [for GDM] and further studies are needed.... Whereas selective screening for GDM may be appropriate in some settings...universal screening may be more appropriate in others.”9 In a major position reversal, the American Diabetes Association’s “Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus,” pub-
Danilenko-Dixon et al 799
Volume 181, Number 4 Am J Obstet Gynecol
Table I. Application of American Diabetes Association criteria for GDM screen exemption General obstetric population (n = 18,504) Exemption criterion Age <25 y Pregravid BMI <27 kg/m2 White, non-Hispanic Negative family history All of above (screen exempt)
Patients with GDM (n = 564)
No.
%
No.
%
Statistical significance
3294 14,359 17,135 17,079 1832
17.8 77.6 92.6 92.3 9.9
54 298 518 436 17
9.6 52.8 91.8 77.3 3.0
P < .001 P < .001 NS P < .001 P < .001
NS, Not significant.
Table II. Diabetes risk factors in general obstetric population and in patients with GDM Risk factor Age, y (mean ± SD) ≥25 y ≥30 y BMI (kg/m2) >25 >27 Race-ethnicity White African American Asian Hispanic Other Family history of diabetes mellitus Smoker Prior GDM Prior infant >4000 g Prior fetal death
General population (n = 18,504)
Patients with GDM (n = 564)
Statistical significance
28.8 ± 5.3 82.2% 51.2% 24.3 ± 5.1 33% 22%
31.3 ± 4.9 90.4% 65.8% 27.5 ± 6.8 58% 47%
P < .001 P < .001 P < .001 P < .0l P < .01 P < .01
92.6% 0.7% 4.9% 1.7% 0.1% 7.7% 11.4% 2.1% 14.5% 0.5%
91.8% 1.4% 4.1% 1.1% 1.6% 22.7% 16.0% 19.4% 29.2% 2.7%
NS — — — — P < .001 P < .05 P < .001 P < .001 P < .001
NS, Not significant.
lished in July 1997, stated, “There are certain factors that place women at lower risk for the development of glucose intolerance during pregnancy, and it is likely not cost-effective to screen such patients.” This low-risk group was defined as women meeting all the following criteria: ≤25 years old; normal body weight, defined as body mass index (BMI) of <27 kg/m2; not a member of a racial or ethnic group with a high prevalence of type 2 diabetes; and no first-degree relatives with diabetes.10 These selective screening criteria were subsequently endorsed by the Fourth International WorkshopConference on Gestational Diabetes.1 The purposes of this study were to determine (1) what proportion of patients with GDM would remain undiagnosed and (2) what proportion of the general obstetric population would be exempt from screening if the selective GDM screening criteria proposed by the American Diabetes Association were retrospectively applied to our universally screened obstetric population. Methods Since January 1, 1986, all women receiving obstetric care at the Mayo Clinic (Rochester, Minnesota) have
been screened for GDM between 24 and 30 weeks’ gestation by determination of the blood glucose level 1 hour after a 50-g oral glucose challenge administered after an overnight fast. Women with screening results of ≥140 mg/dL underwent a 3-hour, 100-g oral glucose tolerance test. Diagnosis of GDM was based on National Diabetes Data Group criteria—at least 2 plasma glucose determinations that met or exceeded 105 mg/dL (5.9 mmol/L) at fasting, 190 mg/dL (10.6 mmol/L) at 1 hour, 165 mg/dL (9.2 mmol/L) at 2 hours, and 145 mg/dL (8.1 mmol/L) at 3 hours.11 Glucose analysis was performed by the Beckman glucose oxidase method with the Beckman CX3 before 1994 and by the hexokinase method with the Hitachi 911 glucose analyzer from 1994 to the present. Between January 1, 1986, and December 31, 1997, 18,834 women were screened for GDM within the institution’s endocrine testing unit. Clinical and demographic data on these women were obtained through the obstetric department’s perinatal database. In 330 patients data on one or more of the American Diabetes Association low-risk criteria were missing, leaving 18,504 for inclusion in the study. Twenty percent of the study population
800 Danilenko-Dixon et al
October 1999 Am J Obstet Gynecol
Fig 1. Cumulative proportion of our general obstetric population who would require screening for GDM on basis of sequential application of risk factors. Age thresholds of ≥25 years and ≥30 years are depicted separately.
Fig 2. Cumulative proportion of our GDM population who would require screening for GDM on basis of sequential application of risk factors. Age thresholds of ≥25 years and ≥30 years are depicted separately.
(3683 women) had a positive GDM screening test result and underwent a 3-hour glucose tolerance test. Three percent of the study population (564 women) met criteria for diagnosis of GDM. Prior fetal death was defined as unexplained in utero fetal death at a gestational age of ≥20 weeks. BMI calculation was based on the pregravid weight recorded in the prenatal record. Statistical analyses consisted of 2-sample t tests for comparison of mean ages and BMIs; χ2 analyses were performed for the remaining binomial variables. P < .05 was required for statistical significance.
Results Results of application of the 1997 American Diabetes Association GDM screening criteria to our obstetric population are presented in Table I. Of 564 cases of GDM diagnosed during the study period, 3% (17 cases) would have been exempt from screening and therefore misdiagnosed. Despite the fact that 93% of our obstetric population is non-Hispanic white, only 9.9% would have been exempt from screening on the basis of all 4 criteria. Table II compares the prevalence of clinical and historical risk factors for GDM in our general obstetric and GDM populations. Consistent with prior published co-
Volume 181, Number 4 Am J Obstet Gynecol
horts, women with GDM were significantly older, more obese, more likely to have a family history of diabetes, more likely to smoke, more likely to have had prior GDM, and more likely to have had a macrosomic or stillborn infant. Figs 1 and 2 depict the cumulative proportions of the general obstetric and GDM populations, respectively, who would require GDM screening on the basis of the sequential application of risk factor criteria. In both Figs 1 and 2, age ≥25 years and age ≥30 years are depicted as separate risk factors. As illustrated in Fig 2, age is clearly the most significant risk factor for GDM in our population. The lower screening threshold of age ≥25 years identifies approximately 25% more patients with GDM than a threshold of age ≥30 years. The remaining risk factors (obesity, family history, and race-ethnicity) add little to the identification of patients with GDM in our population, particularly after a screening threshold of age ≥25 years has been applied. Fig 1 illustrates a similar picture when the same criteria are applied to our general obstetric population. Only 17.8% would be exempt from screening on the basis of age <25 years, whereas 48.8% would be exempt on the basis of age <30 years. Again, relatively few additional screens would result from application of the remaining 3 risk factors in our general population. The age-specific incidence of GDM in this cohort was 1.6% for those aged <25 years and 3.4% for those aged ≥25 years. Comment Recommendations for GDM screening have varied widely, with little consensus among the various clinical organizations and a lack of consistency over time. Whereas universal screening for GDM has been the traditional position advocated by the American Diabetes Association, as well as the First through Third International Workshop-Conferences on GDM,4-7 ACOG has traditionally shied away from recommending universal screening.8, 9 Selective screening protocols based on a variety of risk factors have been endorsed by ACOG and numerous other publications. Maternal age appears to be the most consistent risk factor on which selective screening is based. Twenty-five years ago, O’Sullivan et al12 reported that, although maternal obesity, birth of a prior macrosomic infant, and a family history of diabetes were insensitive predictors of GDM, age ≥25 years was a highly significant risk factor. A number of subsequent investigations have concluded that maternal age is highly correlated with the risk of GDM, but consensus is lacking regarding the appropriate age threshold for screening.13-15 The 1986 ACOG recommendation for selective GDM screening advocated screening women aged ≥30 years, as well as younger women who had traditional clinical or historical risk factors.8 In a population-based application
Danilenko-Dixon et al 801
of the 1986 ACOG screening criteria to 6214 universally screened women, Coustan et al16 reported that 35% of patients with GDM would have been missed by the ACOG protocol while saving only $32 (in 1987 dollars) per case diagnosed compared with universal screening. In the latter study, of 125 GDM cases, 22% of patients were <25 years old and 56% were <30 years old compared with 10% and 34%, respectively, in our cohort. The greater influence of age as a risk factor in our population may be a reflection of much greater racial-ethnic diversity in the cohort of Coustan et al.16 Under the 1986 ACOG recommendations, 56% of our general obstetric population would have been exempt from GDM screening compared with only 10% under the American Diabetes Association guidelines, largely because a substantial proportion of our population falls between the ages of 25 and 30 years. A more recent study investigating the merits of selective screening for GDM concluded, by means of multivariate analysis, that maternal age, race, and prepregnancy BMI were independent predictors of GDM.15 The authors devised a complex scoring system combining clinical risk factors with varying screening thresholds that were based on time elapsed since the last meal. They reported a 34.6% reduction in the number of screening tests with an 81% to 82% GDM detection rate. However, as the accompanying editorial stated, the complexity of this screening tool will likely result in default to universal GDM screening “as a matter of practical convenience.”17 Our obstetric population is unique in its lack of racial and ethnic diversity. Given that non-Hispanic white subjects composed 93% of this cohort, it is not surprising that race-ethnicity was not a significant predictor of GDM in this study. The small number of nonwhite women in this study makes it impossible to analyze race-ethnicity as a risk factor. However, compared with the entire US obstetric population, a greater proportion of our cohort should have been exempt on this basis. Nonetheless, despite its racial and ethnic homogeneity, 90% of our population would have required screening under the American Diabetes Association guidelines. A second unique characteristic of our cohort is the relatively high proportion of older women. Given that only 17.8% of this cohort were <25 years old, age contributed significantly to the proportion requiring GDM screening under the American Diabetes Association recommendations and may have overshadowed the potential contributions of the other 3 risk factors. In our population, age ≥25 years appeared to be the factor most predictive of GDM, in that 90.4% of patients with GDM met this criterion. At the same time, youth, specifically, age <25 years, appeared to offer significant protection against GDM. The remaining 3 screen-exempt criteria proposed by the American Diabetes
802 Danilenko-Dixon et al
Association, specifically, BMI <27 kg/m2, absence of firstdegree relatives with diabetes, and non-Hispanic white race-ethnicity, appeared to add little to the ability of age alone to predict the absence of GDM. This may be somewhat specific to our population, however, in that 82% of our population were aged ≥25 years and would have required screening on this basis alone. In populations with a higher proportion of younger women or with greater racial-ethnic diversity, other factors, such as obesity or ethnicity, may prove more significant in predicting GDM. Application of the American Diabetes Association GDM screening criteria to other populations will be necessary to determine whether the observed protective effects of youth are specific to our obstetric population or applicable to other populations in the United States. With respect to the practical application of selective screening protocols in general, the greater the number and complexity of criteria, the greater the risk of misclassification and error. Whereas, in general, age and race are readily available clinical information, calculation of a woman’s BMI and elicitation of her family history are generally more time-consuming, less readily available, and subject to historical, mathematic, or interpretive errors. Application of the American Diabetes Association screening criteria would add significant complexity, as well as room for error, to the GDM screening process. Moreover, application of these screening guidelines would have resulted in “selective” screening of 90% of our population. Therefore the American Diabetes Association guidelines are so inclusive as to offer no advantage over universal screening. REFERENCES
1. Metzger BE, Coustan DR, The Organizing Committee. Summary and recommendations of the Fourth International Workshop-Conference on Gestational Diabetes Mellitus. Diabetes Care 1998;21:B161-7.
October 1999 Am J Obstet Gynecol
2. O’Sullivan JB, Mahan CM. Criteria for the oral glucose tolerance test in pregnancy. Diabetes 1964;13:278-85. 3. Jarrett RJ. Gestational diabetes: a non-entity? BMJ 1993;306:378. 4. Gestational diabetes mellitus. American Diabetes Association position statement. Diabetes Care 1986;4:430-1. 5. Freinkel N, Josimovich J. Conference Planning Committee: American Diabetes Association Workshop-Conference on Gestational Diabetes: summary and recommendations. Diabetes Care 1980;3:499-501. 6. Freinkel N. Summary and recommendations of the Second International Workshop-Conference on Gestational Diabetes mellitus. Diabetes 1985;34 Suppl 2:123-6. 7. Metzger BE. Summary and recommendations of the Third International Workshop-Conference on Gestational Diabetes Mellitus. Diabetes 1991;40 Suppl 2:197-201. 8. American College of Obstetricians and Gynecologists. Management of diabetes mellitus in pregnancy. Washington: The College; 1986. ACOG Technical Bulletin No.: 92. 9. American College of Obstetricians and Gynecologists. Diabetes and pregnancy. Washington: The College; 1994. ACOG Technical Bulletin No.: 200. 10. The Expert Committee on the diagnosis and classification of diabetes mellitus. Report of the Expert Committee on the diagnosis and classification of diabetes mellitus. Diabetes Care 1997;20:1183-97. 11. National Diabetes Data Group. Classification and diagnosis of diabetes mellitus and other categories of glucose intolerance. Diabetes 1979;28:1039-57. 12. O’Sullivan JB, Mahan CM, Charles D, Dandrow RV. Screening criteria for high-risk gestational diabetic patients. Am J Obstet Gynecol 1973;116:895-900. 13. Sacks DA, Abu-Fadil S, Karten GJ, Forsythe AB, Hackett JR. Screening for gestational diabetes with the one-hour 50-g glucose test. Obstet Gynecol 1987;70:89-93. 14. Solomon CG, Willett WC, Carey VJ, Rich-Edwards J, Hunter DJ, Colditz GA, et al. A prospective study of pregravid determinants of gestational diabetes mellitus. JAMA 1997;278:1078-83. 15. Naylor CD, Sermer M, Chen E, Farine D, for the Toronto Trihospital Gestational Diabetes Project Investigators. Selective screening for gestational diabetes mellitus. N Engl J Med 1997;337:1591-6. 16. Coustan DR, Nelson C, Carpenter MW, Carr SR, Rotondo L, Widness JA. Maternal age and screening for gestational diabetes: a population-based study. Obstet Gynecol 1989;73: 557-61. 17. Greene MF. Screening for gestational diabetes mellitus [letter]. N Engl J Med 1997;337:1625-6.
Key words: Gestational diabetes mellitus screening, American Diabetes Association recommendations
Gestational diabetes mellitus (GDM) is defined as “carbohydrate intolerance of variable severity, with onset or first recognition during pregnancy.”1 Its incidence is highly population-specific, but in general 3% to 5% of pregnant women in this country receive this diagnosis. GDM was initially described in 1964 by O’Sullivan and Mahan,2 with documentation of the association between results of an oral glucose tolerance test during pregnancy and the future development of type 2 diabetes. Subsequently, GDM was associated with stillbirth, macrosomia, shoulder dystocia, birth trauma, need for operative delivery, neonatal hypoglycemia, and other perinatal morbidities. Despite >30 years of research, lack of consensus remains regarding nearly every clinical aspect of GDM—
From the Departments of Obstetrics and Gynecology and Endocrinology, Mayo Clinic. Presented at the Nineteenth Annual Meeting of the Society for MaternalFetal Medicine, San Francisco, California, January 18-23, 1999. Reprint requests: Diana R. Danilenko-Dixon, MD, Maternal-Fetal Medicine, Mayo Clinic, 200 First St SW, Rochester, MN 55905. Copyright © 1999 by Mosby, Inc. 0002-9378/99 $8.00 + 0 6/6/100571
798
the need to screen, diagnostic criteria, treatment, and even the validity of GDM as a meaningful diagnosis.3 Traditionally, universal screening of all pregnant women for GDM had been endorsed by both the American Diabetes Association Position Statement and by the First, Second, and Third International Workshop-Conferences on GDM.4-7 Meanwhile, The American College of Obstetricians and Gynecologists (ACOG) 1986 Technical Bulletin recommended selective screening for GDM for women ≥30 years old or for younger women with clinical or historical risk factors, such as prior GDM, obesity, family history of diabetes, or a prior macrosomic, anomalous, or stillborn infant.8 The more recent 1994 ACOG Technical Bulletin on diabetes and pregnancy fell short of recommending universal GDM screening, stating, “There are no data to support the benefit of screening [for GDM] and further studies are needed.... Whereas selective screening for GDM may be appropriate in some settings...universal screening may be more appropriate in others.”9 In a major position reversal, the American Diabetes Association’s “Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus,” pub-
Danilenko-Dixon et al 799
Volume 181, Number 4 Am J Obstet Gynecol
Table I. Application of American Diabetes Association criteria for GDM screen exemption General obstetric population (n = 18,504) Exemption criterion Age <25 y Pregravid BMI <27 kg/m2 White, non-Hispanic Negative family history All of above (screen exempt)
Patients with GDM (n = 564)
No.
%
No.
%
Statistical significance
3294 14,359 17,135 17,079 1832
17.8 77.6 92.6 92.3 9.9
54 298 518 436 17
9.6 52.8 91.8 77.3 3.0
P < .001 P < .001 NS P < .001 P < .001
NS, Not significant.
Table II. Diabetes risk factors in general obstetric population and in patients with GDM Risk factor Age, y (mean ± SD) ≥25 y ≥30 y BMI (kg/m2) >25 >27 Race-ethnicity White African American Asian Hispanic Other Family history of diabetes mellitus Smoker Prior GDM Prior infant >4000 g Prior fetal death
General population (n = 18,504)
Patients with GDM (n = 564)
Statistical significance
28.8 ± 5.3 82.2% 51.2% 24.3 ± 5.1 33% 22%
31.3 ± 4.9 90.4% 65.8% 27.5 ± 6.8 58% 47%
P < .001 P < .001 P < .001 P < .0l P < .01 P < .01
92.6% 0.7% 4.9% 1.7% 0.1% 7.7% 11.4% 2.1% 14.5% 0.5%
91.8% 1.4% 4.1% 1.1% 1.6% 22.7% 16.0% 19.4% 29.2% 2.7%
NS — — — — P < .001 P < .05 P < .001 P < .001 P < .001
NS, Not significant.
lished in July 1997, stated, “There are certain factors that place women at lower risk for the development of glucose intolerance during pregnancy, and it is likely not cost-effective to screen such patients.” This low-risk group was defined as women meeting all the following criteria: ≤25 years old; normal body weight, defined as body mass index (BMI) of <27 kg/m2; not a member of a racial or ethnic group with a high prevalence of type 2 diabetes; and no first-degree relatives with diabetes.10 These selective screening criteria were subsequently endorsed by the Fourth International WorkshopConference on Gestational Diabetes.1 The purposes of this study were to determine (1) what proportion of patients with GDM would remain undiagnosed and (2) what proportion of the general obstetric population would be exempt from screening if the selective GDM screening criteria proposed by the American Diabetes Association were retrospectively applied to our universally screened obstetric population. Methods Since January 1, 1986, all women receiving obstetric care at the Mayo Clinic (Rochester, Minnesota) have
been screened for GDM between 24 and 30 weeks’ gestation by determination of the blood glucose level 1 hour after a 50-g oral glucose challenge administered after an overnight fast. Women with screening results of ≥140 mg/dL underwent a 3-hour, 100-g oral glucose tolerance test. Diagnosis of GDM was based on National Diabetes Data Group criteria—at least 2 plasma glucose determinations that met or exceeded 105 mg/dL (5.9 mmol/L) at fasting, 190 mg/dL (10.6 mmol/L) at 1 hour, 165 mg/dL (9.2 mmol/L) at 2 hours, and 145 mg/dL (8.1 mmol/L) at 3 hours.11 Glucose analysis was performed by the Beckman glucose oxidase method with the Beckman CX3 before 1994 and by the hexokinase method with the Hitachi 911 glucose analyzer from 1994 to the present. Between January 1, 1986, and December 31, 1997, 18,834 women were screened for GDM within the institution’s endocrine testing unit. Clinical and demographic data on these women were obtained through the obstetric department’s perinatal database. In 330 patients data on one or more of the American Diabetes Association low-risk criteria were missing, leaving 18,504 for inclusion in the study. Twenty percent of the study population
800 Danilenko-Dixon et al
October 1999 Am J Obstet Gynecol
Fig 1. Cumulative proportion of our general obstetric population who would require screening for GDM on basis of sequential application of risk factors. Age thresholds of ≥25 years and ≥30 years are depicted separately.
Fig 2. Cumulative proportion of our GDM population who would require screening for GDM on basis of sequential application of risk factors. Age thresholds of ≥25 years and ≥30 years are depicted separately.
(3683 women) had a positive GDM screening test result and underwent a 3-hour glucose tolerance test. Three percent of the study population (564 women) met criteria for diagnosis of GDM. Prior fetal death was defined as unexplained in utero fetal death at a gestational age of ≥20 weeks. BMI calculation was based on the pregravid weight recorded in the prenatal record. Statistical analyses consisted of 2-sample t tests for comparison of mean ages and BMIs; χ2 analyses were performed for the remaining binomial variables. P < .05 was required for statistical significance.
Results Results of application of the 1997 American Diabetes Association GDM screening criteria to our obstetric population are presented in Table I. Of 564 cases of GDM diagnosed during the study period, 3% (17 cases) would have been exempt from screening and therefore misdiagnosed. Despite the fact that 93% of our obstetric population is non-Hispanic white, only 9.9% would have been exempt from screening on the basis of all 4 criteria. Table II compares the prevalence of clinical and historical risk factors for GDM in our general obstetric and GDM populations. Consistent with prior published co-
Volume 181, Number 4 Am J Obstet Gynecol
horts, women with GDM were significantly older, more obese, more likely to have a family history of diabetes, more likely to smoke, more likely to have had prior GDM, and more likely to have had a macrosomic or stillborn infant. Figs 1 and 2 depict the cumulative proportions of the general obstetric and GDM populations, respectively, who would require GDM screening on the basis of the sequential application of risk factor criteria. In both Figs 1 and 2, age ≥25 years and age ≥30 years are depicted as separate risk factors. As illustrated in Fig 2, age is clearly the most significant risk factor for GDM in our population. The lower screening threshold of age ≥25 years identifies approximately 25% more patients with GDM than a threshold of age ≥30 years. The remaining risk factors (obesity, family history, and race-ethnicity) add little to the identification of patients with GDM in our population, particularly after a screening threshold of age ≥25 years has been applied. Fig 1 illustrates a similar picture when the same criteria are applied to our general obstetric population. Only 17.8% would be exempt from screening on the basis of age <25 years, whereas 48.8% would be exempt on the basis of age <30 years. Again, relatively few additional screens would result from application of the remaining 3 risk factors in our general population. The age-specific incidence of GDM in this cohort was 1.6% for those aged <25 years and 3.4% for those aged ≥25 years. Comment Recommendations for GDM screening have varied widely, with little consensus among the various clinical organizations and a lack of consistency over time. Whereas universal screening for GDM has been the traditional position advocated by the American Diabetes Association, as well as the First through Third International Workshop-Conferences on GDM,4-7 ACOG has traditionally shied away from recommending universal screening.8, 9 Selective screening protocols based on a variety of risk factors have been endorsed by ACOG and numerous other publications. Maternal age appears to be the most consistent risk factor on which selective screening is based. Twenty-five years ago, O’Sullivan et al12 reported that, although maternal obesity, birth of a prior macrosomic infant, and a family history of diabetes were insensitive predictors of GDM, age ≥25 years was a highly significant risk factor. A number of subsequent investigations have concluded that maternal age is highly correlated with the risk of GDM, but consensus is lacking regarding the appropriate age threshold for screening.13-15 The 1986 ACOG recommendation for selective GDM screening advocated screening women aged ≥30 years, as well as younger women who had traditional clinical or historical risk factors.8 In a population-based application
Danilenko-Dixon et al 801
of the 1986 ACOG screening criteria to 6214 universally screened women, Coustan et al16 reported that 35% of patients with GDM would have been missed by the ACOG protocol while saving only $32 (in 1987 dollars) per case diagnosed compared with universal screening. In the latter study, of 125 GDM cases, 22% of patients were <25 years old and 56% were <30 years old compared with 10% and 34%, respectively, in our cohort. The greater influence of age as a risk factor in our population may be a reflection of much greater racial-ethnic diversity in the cohort of Coustan et al.16 Under the 1986 ACOG recommendations, 56% of our general obstetric population would have been exempt from GDM screening compared with only 10% under the American Diabetes Association guidelines, largely because a substantial proportion of our population falls between the ages of 25 and 30 years. A more recent study investigating the merits of selective screening for GDM concluded, by means of multivariate analysis, that maternal age, race, and prepregnancy BMI were independent predictors of GDM.15 The authors devised a complex scoring system combining clinical risk factors with varying screening thresholds that were based on time elapsed since the last meal. They reported a 34.6% reduction in the number of screening tests with an 81% to 82% GDM detection rate. However, as the accompanying editorial stated, the complexity of this screening tool will likely result in default to universal GDM screening “as a matter of practical convenience.”17 Our obstetric population is unique in its lack of racial and ethnic diversity. Given that non-Hispanic white subjects composed 93% of this cohort, it is not surprising that race-ethnicity was not a significant predictor of GDM in this study. The small number of nonwhite women in this study makes it impossible to analyze race-ethnicity as a risk factor. However, compared with the entire US obstetric population, a greater proportion of our cohort should have been exempt on this basis. Nonetheless, despite its racial and ethnic homogeneity, 90% of our population would have required screening under the American Diabetes Association guidelines. A second unique characteristic of our cohort is the relatively high proportion of older women. Given that only 17.8% of this cohort were <25 years old, age contributed significantly to the proportion requiring GDM screening under the American Diabetes Association recommendations and may have overshadowed the potential contributions of the other 3 risk factors. In our population, age ≥25 years appeared to be the factor most predictive of GDM, in that 90.4% of patients with GDM met this criterion. At the same time, youth, specifically, age <25 years, appeared to offer significant protection against GDM. The remaining 3 screen-exempt criteria proposed by the American Diabetes
802 Danilenko-Dixon et al
Association, specifically, BMI <27 kg/m2, absence of firstdegree relatives with diabetes, and non-Hispanic white race-ethnicity, appeared to add little to the ability of age alone to predict the absence of GDM. This may be somewhat specific to our population, however, in that 82% of our population were aged ≥25 years and would have required screening on this basis alone. In populations with a higher proportion of younger women or with greater racial-ethnic diversity, other factors, such as obesity or ethnicity, may prove more significant in predicting GDM. Application of the American Diabetes Association GDM screening criteria to other populations will be necessary to determine whether the observed protective effects of youth are specific to our obstetric population or applicable to other populations in the United States. With respect to the practical application of selective screening protocols in general, the greater the number and complexity of criteria, the greater the risk of misclassification and error. Whereas, in general, age and race are readily available clinical information, calculation of a woman’s BMI and elicitation of her family history are generally more time-consuming, less readily available, and subject to historical, mathematic, or interpretive errors. Application of the American Diabetes Association screening criteria would add significant complexity, as well as room for error, to the GDM screening process. Moreover, application of these screening guidelines would have resulted in “selective” screening of 90% of our population. Therefore the American Diabetes Association guidelines are so inclusive as to offer no advantage over universal screening. REFERENCES
1. Metzger BE, Coustan DR, The Organizing Committee. Summary and recommendations of the Fourth International Workshop-Conference on Gestational Diabetes Mellitus. Diabetes Care 1998;21:B161-7.
October 1999 Am J Obstet Gynecol
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