Share this article on:

Gestational Diabetes Screening: The International Association of the Diabetes and Pregnancy Study Groups Compared With Carpenter-Coustan Screening

Feldman, R. Klara MD; Tieu, Ryan S. MS; Yasumura, Lyn MD

doi: 10.1097/AOG.0000000000001132
Contents: Original Research
Journal Club
Correction
Annual Awards

OBJECTIVE: To evaluate whether one-step gestational diabetes screening recommended by The International Association of the Diabetes and Pregnancy Study Groups (IADPSG) is associated with better maternal, perinatal, or neonatal outcomes than the two-step Carpenter-Coustan screening.

METHODS: In this before–after retrospective cohort study conducted between July 1, 2010, and December 31, 2013, we compared Carpenter-Coustan and IADPSG screening in patients with singleton pregnancies. All patients diagnosed with gestational diabetes received intensive teaching, home glucose monitoring, and medications as indicated. The primary outcome was the rate of large-for-gestational-age neonates. Secondary outcome measures were macrosomia (greater than 4,000 g), primary cesarean delivery, neonatal intensive care unit admission, preterm delivery, preeclampsia, and hyperbilirubinemia. We determined that a sample size of 2,782 per group was sufficient to detect a 2% difference in the primary outcome between groups with 80% power assuming a 10% incidence in the before group. The groups were compared using Fisher exact test for proportions and a χ2 test for odds ratios.

RESULTS: In the before (Carpenter-Coustan) group, 513 (17%) of the 2,972 patients were diagnosed with gestational diabetes, and in the after (IADPSG) group, 847 (27%) of the 3,094 patients were so diagnosed (P<.001). There was no significant difference in rates of large for gestational age, 10% and 9%, respectively (P=.25). The IADPSG group had a significantly higher primary cesarean delivery rate—16% compared with 20% (P<.001), but there were no significant differences in any other pregnancy outcomes.

CONCLUSION: Although one-step screening was associated with more patients being treated for gestational diabetes, it was not associated with a decrease in large-for-gestational-age or macrosomic neonates but was associated with an increased rate of primary cesarean delivery. Our results did not support the IADPSG-recommended screening protocol.

The International Association of the Diabetes and Pregnancy Study Groups' screening method for gestational diabetes is not associated with a reduction in large-for-gestational-age newborns or cesarean deliveries but is associated with a higher rate of gestational diabetes.

Departments of Obstetrics and Gynecology, Kaiser Permanente at Baldwin Park, Montebello, and Kaiser Permanente Baldwin Park Medical Center, Baldwin Park, and the Department of Research and Evaluation, Kaiser Permanente, Pasadena, California.

Corresponding author: R. Klara Feldman, MD, Department of Obstetrics and Gynecology, Kaiser Permanente at Baldwin Park, 1550 Town Center Drive, Montebello, CA 90640; e-mail: klara.r.feldman@kp.org.

Supported by the Kaiser Permanente Regional Research Committee.

Financial Disclosure The authors did not report any potential conflicts of interest.

The authors thank Kevin Mau, MS, for his assistance with statistical analysis and Carol Walden, RN, for her data collection and case management.

Gestational diabetes has been associated with preterm delivery, preeclampsia, macrosomia (birth weight greater than 4,000 g), increased risk of cesarean delivery for arrest disorders, shoulder dystocia, neonatal hyperbilirubinemia, and respiratory distress syndrome1–5 as well as the later development of noninsulin-dependent diabetes mellitus.6 Some studies show an association between fetal exposure to uncontrolled maternal blood glucose and subsequent neonatal and childhood obesity.7,8

Much controversy exists about how to identify gestational diabetes and whether the benefits of intervention justify the expense, the anxiety, and the possible risks associated with this diagnosis. For many years, health care providers in the United States have screened for gestational diabetes using a two-step test early in gestation in those patients deemed to be at high risk and a second test at 24–28 weeks of gestation to average-risk patients.9 Values were considered abnormal if they exceeded those recommended by either the Carpenter and Coustan10 and Fourth International Workshop-Conference Criteria11 or the values designated by the National Diabetes Data Group.12 The American College of Obstetricians and Gynecologists continues to recommend this two-step approach.

Based on observational studies that specifically evaluated maternal, perinatal, and neonatal outcomes, The International Association of the Diabetes and Pregnancy Study Groups (IADPSG) and the World Health Organization recommended new criteria for the diagnosis of gestational diabetes.13 They recommend that a hemoglobin A1C (Hb A1c), a random plasma glucose, or a fasting plasma glucose test be performed at the first prenatal visit to identify undiagnosed pregestational diabetics and that a one-step 2-hour glucose tolerate test with a 75-g glucose load be performed at 24–28 weeks of gestation for those not identified as having pregestational diabetes.

In this study we sought to address whether changing from the traditional two-step Carpenter-Coustan screening recommended by the American College of Obstetricians and Gynecologists to the one-step test recommended by The International Association of Diabetes and Pregnancy Study Groups would be associated with meaningful improvements in maternal, perinatal, or neonatal outcomes.

Back to Top | Article Outline

MATERIALS AND METHODS

In November 2011, our hospital and affiliated clinics switched from the two-step Carpenter-Coustan screening approach to the one-step approach recommended by the IADPSG. We performed a before–after retrospective cohort study that compared patients before and after the change. We extracted demographic and obstetric data from the electronic medical record and verified it by selective chart review.

The sample consists of singleton pregnancies managed from the first trimester within the Kaiser Permanente Baldwin Park Medical Center and its affiliated clinics between July 1, 2010, and December 31, 2013. Mothers who were classified as diabetic before pregnancy were excluded. To keep the before and after groups statistically independent, patients were excluded if they had more than one pregnancy in the study period.

For the primary outcome of large birth weight for gestational age and sex (LGA), we determined that a sample size of 5,564 (2,782 per group) would allow the detection of an absolute rate difference of 2% between groups assuming a rate of 10% in the before group with 80% power at the 0.05 (two-tailed) significance level.

Figures 1 and 2, respectively, illustrate the screening protocols used in the before and after groups. Patients with Hb A1c levels of 6.5% or higher were considered to have overt diabetes. Because they had not been diagnosed with diabetes before the pregnancy, they were included in our treatment group and for statistical purposes were also categorized as having gestational diabetes. These patients were not excluded because our before group likely also had some patients with undiagnosed overt prepregnancy diabetes. Patients with Hb A1c levels between 5.7 and 6.4 were diagnosed with prediabetes and were treated in a similar manner as those having gestational diabetes. For statistical purposes, they were also included with those having gestational diabetes.

Fig. 1

Fig. 1

Fig. 2

Fig. 2

The care of patients with gestational diabetes did not change over the time course of the study. Patients attended a nutrition class and began home glucose monitoring with a fasting and three postprandial tests. The patients were seen in the office every 1–4 weeks at the discretion of their health care provider. Typically, if more than one third of the fasting results was greater than 95 mg/dL or one third of the postprandial tests greater than 130 mg/dL at 1 hour or 120 mg/dL at 2 hours, the patients were started on either insulin or glyburide at the discretion of their health care provider. During this study metformin was used only in isolated cases. Patients who were prescribed any medication were monitored with twice-weekly fetal nonstress tests and amniotic fluid index measurement from 34 to 36 weeks of gestation to delivery. Patients who required medication were induced at 39 weeks of gestation if they had not gone into labor spontaneously. Patients who did not require medication were induced by 42 weeks of gestation.

We described the characteristics of the before and after groups using means with standard deviations or medians with interquartile regions for continuous variables. For discrete variables, we used percentages and counts. P values were obtained using Fisher test for proportions and Wilcoxon for continuous variables.

The primary study outcome was LGA, defined as a birth weight greater than the 90th percentile for gestational age and sex. The odds ratio between the two groups was computed, and an unadjusted comparison of the before and after groups was done using a χ2 test. We used a logistic regression model to compare the two groups adjusting for certain covariates.

Secondary outcomes included neonatal intensive care unit admission, preterm delivery (before 37 weeks of gestation), preeclampsia, and hyperbilirubinemia (which was inferred if phototherapy was used). A secondary analysis was performed to evaluate the association of body mass index (BMI, calculated as weight (kg)/[height (m)]2) with the primary and secondary outcome measures. Body mass index was treated as a continuous variable. We used a logistic regression model to adjust for certain covariates.

This study was approved by the Kaiser Permanente Southern California institutional review board.

Back to Top | Article Outline

RESULTS

After exclusions, the final sample included 6,066 pregnancies (2,972 before protocol change and 3,094 after protocol change; Fig. 3; Table 1). The average maternal age of the two groups was 30 years. The median BMI at the first prenatal care visit for both groups was not significantly different. There was a greater proportion of patients with gestational diabetes mellitus in the after group (27% compared with 17%, P<.001) and more patients being diagnosed with prediabetes (15% compared with 4%, P<.001). There was no significant difference in rates of LGA, 10% in the before group and 9% in the after, respectively (P=.25). No significant difference was noted in the median number of perinatal encounters or in the proportion of patients who underwent labor induction. Although no significant difference existed in the number of patients being treated with metformin, a greater number was treated with insulin and glyburide in the after group. There was no significant difference in prenatal weight at the first prenatal care visit between the two groups (P=.67). Mothers in the before group had a higher median weight than those in the after group both at the last visit before delivery and at the postpartum checkup 4 weeks after the delivery. There was a significant difference between the before and after groups in weight change from the first prenatal care visit to the postpartum checkup. However, this change was too small to be clinically significant.

Fig. 3

Fig. 3

Table 1

Table 1

A significant difference in frequency of cesarean deliveries was noted between the before and after groups, even among patients not diagnosed with gestational diabetes (Table 2). However, there was no significant difference in the adjusted odds of cesarean deliveries resulting from arrest disorders between the two groups. Table 3 shows that the odds of having a primary cesarean delivery were significantly greater in the after group. However, no significant difference was noted in the odds of having LGA (greater than the 90th percentile for age and sex) between the before and after groups. In contrast, a statistically significant difference in LGA neonates, macrosomia, and primary cesarean delivery was noted between patients with different BMIs at the first prenatal visit (Table 4).

Table 2

Table 2

Table 3

Table 3

Table 4

Table 4

Back to Top | Article Outline

DISCUSSION

In our study cohort, the use of the one-step IADPSG protocol for gestational diabetes screening instead of the two-step approach using the Carpenter-Coustan criteria cutoffs was associated with an increase in the rate of gestational diabetes from 17% to 27%. However, the IADPSG approach was not associated with a lower rate of LGA neonates, macrosomia, neonatal intensive care unit admissions, preterm births, preeclampsia, shoulder dystocia, or hyperbilirubinemia.

In contrast, a number of studies have noted that treating patients with glucose intolerance below the Carpenter-Coustan criteria can reduce the number of LGA fetuses. Bonomo et al and Bevier et al showed that treating women with an elevated 50-g glucose challenge test but a normal 100-g glucose tolerance test resulted in fewer LGA neonates.14,15 Crowther et al16 showed that treating women diagnosed with gestational diabetes by a 50- g oral glucose challenge test followed by a 75-g oral glucose tolerance test decreased serious perinatal complications. The IADPSG extrapolated from these studies that expanding the number of patients diagnosed with and treated for gestational diabetes would result in fewer LGA neonates. However, the current study does not support that hypothesis. The cutoffs chosen by the IADPSG, based on the results of the Hyperglycemia and Adverse Pregnancy Outcomes study,17,18 may be too low and thus result in too many patients being treated as having gestational diabetes. Different cutoff values need to be evaluated and more attention needs to be focused on controlling prepregnancy BMI.

Interestingly, this study reaffirmed other studies that found a high correlation between BMI and proportion of LGA neonates.8,19,20 Black et al followed women who were found to have IADPSG-defined gestational diabetes but who were not treated. They found that prepregnancy maternal obesity had a greater effect on the proportion of LGA neonates than did untreated gestational diabetes.19 Di Benedetto et al20 evaluated nondiabetic women and found that those who were obese and overweight had a significantly greater percentage of macrocosmic neonates than women who were not obese and not diabetic. Pettitt et al1 in evaluating gestational diabetes in Pima Indians noted that maternal weight, maternal age, and third-trimester glucose values were so closely related that it was difficult to discern which had the greatest effect. These studies taken together with the current one suggest that a renewed focus on reducing prepregnancy overweight and obesity rates may result in a smaller proportion of LGA neonates.

A strength of this study is that the same physicians treated patients who came from the same community using the same treatment for gestational diabetes for both the before and after time periods. However, this strength may limit the generalizability of the results. The population studied had a majority Hispanic and Pacific Islander and Asian ethnicity. For this population, the rate of gestational diabetes by either testing criteria is higher than what has been reported in other studies with more diverse populations.21 Furthermore, as a retrospective analysis, this study has inherent limitations. Changes in practice patterns do occur over time as noted by the increase in cesarean deliveries even in patients who did not have gestational diabetes. However, the increase in total cesarean deliveries between the before and after groups was even greater. The difference between the increase that can be accounted for by changes in practice pattern and the total increase suggests that changing the testing criteria contributed to the increase in cesarean deliveries. This study grouped patients with prediabetes with those who developed gestational diabetes in the late second trimester. These two groups may be intrinsically different and may require a different treatment approach. A study evaluating the differences between these two groups and how they respond to treatment may result in a smaller proportion of LGA neonates and possibly even cesarean deliveries.

In summary, in this study, the IADPSG screening method for gestational diabetes was not associated with a reduction in LGA newborns or cesarean deliveries but was associated with a higher rate of gestational diabetes.

Back to Top | Article Outline

REFERENCES

1. Pettitt DJ, Knowler WC, Baird HR, Bennett PH. Gestational diabetes: infant and maternal complications of pregnancy in relation to third-trimester glucose tolerance in the Pima Indians. Diabetes Care 1980;3:458–64.
2. Jensen DM, Korsholm L, Ovesen P, Beck-Nielsen H, Mølsted-Pedersen L, Damm P. Adverse pregnancy outcome in women with mild glucose intolerance: is there a clinically meaningful threshold value for glucose? Acta Obstet Gynecol Scand 2008;87:59–62.
3. Sermer M, Naylor CD, Gare DJ, Kenshole AB, Ritchie JW, Farine D, et al.. Impact of increasing carbohydrate intolerance on maternal-fetal outcomes in 3637 women without gestational diabetes. The Toronto Tri-Hospital Gestational Diabetes Project. Am J Obstet Gynecol 1995;173:146–56.
4. Ferrara A, Weiss NS, Hedderson MM, Quesenberry CP Jr, Selby JV, Ergas IJ, et al.. Pregnancy plasma glucose levels exceeding the American Diabetes Association thresholds, but below the National Diabetes Data Group thresholds for gestational diabetes mellitus, are related to the risk of neonatal macrosomia, hypoglycaemia and hyperbilirubinaemia. Diabetologia 2007;50:298–306.
5. American Academy of Pediatrics Subcommittee on Hyperbilirubinemia. Clinical practice guideline. Management of hyperbilirubinemia in the newborn infant 35 or more weeks of gestation. Pediatrics 2004;114:297–316.
6. Bellamy L, Casas JP, Hingorani AD, Williams D. Type 2 diabetes mellitus after gestational diabetes: a systemic review and meta-analysis. Lancet 2009;373:1773–9.
7. Metzger BE. Long-term outcomes in mothers diagnosed with gestational diabetes mellitus and their offspring. Clin Obstet Gynecol 2007;50:972–9.
8. Boney CM, Verma A, Tucker R, Vohr BR. Metabolic syndrome in childhood: association with birth weight, maternal obesity, and gestational diabetes mellitus. Pediatrics 2005;115:e290–6.
9. Gestational diabetes mellitus. Practice Bulletin No. 137. American College of Obstetricians and Gynecologists. Obstet Gynecol 2013;122:406–16.
10. Carpenter MW, Coustan DR. Criteria for screening tests for gestational diabetes. Am J Obstet Gynecol 1982;144:768–73.
11. Metzger BE, Coustan DR. Summary and recommendations of the Fourth International Workshop-Conference on Gestational Diabetes Mellitus. The Organizing Committee. Diabetes Care 1998;21(suppl 2):B161–7.
12. Classification and diagnosis of diabetes mellitus and other categories of glucose tolerance. National Diabetes Data Group. Diabetes 1979;28:1039–57.
13. International Association of Diabetes and Pregnancy Study Groups Consensus Panel, Metzger BE, Gabbe SG, Persson B, Buchanan TA, Catalano PA, et al.. International association of diabetes and pregnancy study groups recommendations on the diagnosis and classification of hyperglycemia in pregnancy. Diabetes Care 2010;33:676–82.
14. Bonomo M, Corica D, Mion E, Goncalves D, Motta G, Merati R, et al.. Evaluating the therapeutic approach in pregnancies complicated by borderline glucose intolerance: a randomized clinical trial. Diabet Med 2005;22:1536–41.
15. Bevier WC, Fischer R, Jovanovic L. Treatment of women with an abnormal glucose challenge test (but a normal oral glucose tolerance test) decreases the prevalence of macrosomia. Am J Perinatol 1999;16:269–75.
16. Crowther CA, Hiller JE, Moss JR, McPhee JA, Jeffries WS, Robinson JS, et al.. Effect of treatment of gestational diabetes mellitus on pregnancy outcomes. N Engl J Med 2005;352:2477–86.
17. HAPO Cooperative Research Group. Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study: associations with neonatal anthropometrics. Diabetes 2009;58:453–9.
18. HAPO Study Cooperative Research Group, Metzger BE, Lowe LP, Dyer AR, Trimble ER, Chaovarindr U, et al.. Hyperglycemia and adverse pregnancy outcomes. N Engl J Med 2008;358:1991–2002.
19. Black MH, Sacks DA, Xiang AH, Lawrence JM. The Relative Contribution of prepregnancy overweight and obesity, gestational weight gain, and IADPSG-defined gestational diabetes mellitus to fetal Overgrowth. Diabetes Care 2013;36:56–62.
20. Di Benedetto A, D'anna R, Cannata ML, Giordano D, Interdonato ML, Corrado F. Effects of prepregnancy body mass index and weight gain during pregnancy on perinatal outcome in glucose-tolerant women. Diabetes Metab 2012;38:63–7.
21. Ferrara A. Increasing prevalence of gestational diabetes mellitus. A public health perspective. Diabetes Care 2007;30(suppl 2):S141–6.
Figure

Figure

© 2016 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.