Glucose challenge test threshold values in screening for gestational diabetes among black women

American Journal of Obstetrics and Gynecology (2006) 194, e46–e48

www.ajog.org

Glucose challenge test threshold values in screeningfor gestational diabetes among black women

Sarah Friedman, MD, Fady Khoury-Collado, MD,* Mudar Dalloul, MD,David M. Sherer, MD, Ovadia Abulafia, MD

Department of Obstetrics and Gynecology, State University of New York, Downstate Medical Center, Brooklyn, NY

Received for publication August 31, 2005; revised February 25, 2006; accepted March 13, 2006

KEY WORDSGestational diabetes

BlackScreening

Objective: The objective of the study was to assess the incidence of gestational diabetes amongblack women according to various cut-off values of the glucose challenge test.Study design: We performed a retrospective chart review of black patients who had a 50-g, 1-hourglucose challenge test between 24 and 28 weeks’ gestation of 130 mg/dL or higher followed by a

100-g, 3-hour glucose tolerance test. Results were categorized in 10-mg/dL increments. Gestationaldiabetes was diagnosed by 2 or more abnormal values using the Carpenter-Coustan criteria.Results: The study included 387 patients. The incidence of gestational diabetes diagnosed overall in

all patients with a glucose challenge test of 130 mg/dL or higher was 31.2%. The incidence of ges-tational diabetes in individuals with a challenge test in the range of 130 to 140 mg/dL was 10.7%.The incidence of gestational diabetes with a screening test of 180 mg/dL or higher was 72.0%.

Conclusion: Our data support the use of 130mg/dL as the threshold for a positive glucose challengetest and suggest the use of a glucose tolerance test to confirm the diagnosis of gestational diabetesfor screening values up to 200 mg/dL.� 2006 Mosby, Inc. All rights reserved.

Laboratory screening for gestational diabetes is mostcommonly performed in the United States with the 50-g,1-hour glucose challenge test between 24 and 28 weeksof gestation.1 A value above 130-140 mg/dL is consid-ered positive and is followed by a 3-hour oral glucosetolerance test (GTT). Gestational diabetes mellitus(GDM) is diagnosed when 2 or more values of theGTT are elevated. Previous reports have noted that,for glucose challenge tests in the range of 180-200 mg/dL, GDM can be diagnosed without the need for aGTT because a GTT would be positive in close to

* Reprint requests: Fady Khoury-Collado, MD, 450 Clarkson

Avenue, Box 24. Brooklyn, NY 11203.

E-mail: FCollado@Downstate.edu

0002-9378/$ - see front matter � 2006 Mosby, Inc. All rights reserved.

doi:10.1016/j.ajog.2006.03.051

100% of those patients.2-4 This assumption has beencontested by other data, especially when examining spe-cific ethnic populations.5,6

The objective of our study was to review the incidenceof GDM diagnosed at different thresholds of the glucosechallenge test in an inner-city black population, consid-ered by previous reports to be a population with anincreased incidence of GDM.7

Material and Methods

We performed a retrospective chart review of blackpatients who had a 50-g, 1-hour glucose challenge testbetween 24 and 28 weeks’ gestation of 130 mg/dL or

Friedman et al e47

Table I Incidence of gestational diabetes in relation to the glucose challenge result

Glucose tolerance test

Glucose challengetest (mg/dL) Normal

1 Abnormalvalue, n

2 Abnormalvalues, n Patients, n

1 Abnormalvalue, %

2 Abnormalvalues, %

130-139 38 12 6 56 21.4 10.7140-149 84 21 20 125 16.8 16.0150-159 38 16 28 82 19.5 34.1160-169 31 3 22 56 5.3 39.2170-179 9 2 14 25 8.0 56.0180-189 4 3 14 21 14.2 66.6190-199 3 2 9 14 14.2 64.2R200 0 0 8 8 0 100.0Total 207 59 121 387 15.2 31.2

Table II Incidence of gestational diabetes for glucose challenge results above 180 mg/dL

Glucose tolerance test

Glucose challengetest, mg/dL Normal 1 Abnormal value 2 Abnormal values Patients, n

1 Abnormalvalue, %

2 Abnormalvalues, %

180-189 4 3 14 21 14.2 66.6190-199 3 2 9 14 14.2 64.2R200 0 0 8 8 0 100.0Total R180 7 5 31 43 11.6 72.0

higher followed by a 100-g, 3-hour GTT. The studyperiod extended from July 1, 2000, to December 31, 2004.

The study was approved by the Institutional ReviewBoard of the State University of New York, DownstateMedical Center (Brooklyn, NY), in which all includedpatients had their prenatal care. Results were categorizedin 10-mg/dL increments, similar to a previous report byYogev et al.5 GDM was diagnosed by 2 or more abnor-mal values using the Carpenter-Coustan criteria.2

Results

The study included 387 patients with singleton fetuses.The average maternal age was 31.6 G 5.9 years. Theaverage gestational age at screening was 26.9 G 1.1weeks. The incidence of GDM diagnosed overall in allpatients with a glucose challenge test of 130 mg/dL orhigher was 31.2%. The incidence of GDM in individualswith a challenge test in the range of 130-140 mg/dL was10.7% (Table I). The incidence of GDM with a screen-ing test of 180 mg/dL or higher was 72.0% (Table II).

Comment

The incidence of GDM following a positive screeningtest (130 mg/dL or above) in our black population was

31.2%. This value is consistent with previous reportsthat showed a higher incidence of GDM in black womenafter a positive glucose challenge test.8,9

In their original report in 1982, Carpenter andCoustan2 reported a probability of GDM of morethan 95% when the glucose challenge test result wasabove 182 mg/dL. Although some subsequent studies3,4

confirmed this finding, others did not: Yogev et al5

found an incidence of GDM of only 57% in Mexican-American women when the challenge test was above200 mg/dL; Shivvers and Lucas6 found an incidence ofGDM of 81% when the challenge test was above 200mg/dL and even reported a case of normal GTT witha challenge test of 256 mg/dL. Added to the potentiallyincreased anxiety created to the patient, pregnancy com-plicated by GDM requires intense monitoring that willsignificantly add to the cost of the care of the pregnancyand can even lead to nonindicated interventions (ie, ce-sarean delivery for macrosomia). Therefore, overdiag-nosing GDM may not be without consequences.

Although considered a higher risk group for GDM,7

our population of pregnant black women had only a72.0% incidence of GDM when the glucose challengetest result was above 180 mg/dL. The incidence ofGDM reached 100% only when the screening test wasabove 200 mg/dL. Of note, we had only 8 patients inthis category. Langer et al10 previously reported thatpregnant patients with only 1 abnormal value on the

e48 Friedman et al

GTT have an increased risk of adverse perinatal out-come that can be reduced with strict glucose control.In our population, even when we included patientswith 1 abnormal value on the GTT in the GDM cate-gory, the incidence of GDM increased to only 83.6%when the challenge test was 180 mg/dL or higher.Thus, our results support obtaining a GTT when thescreening test is in the range of 180-200 mg/dL to avoida significant proportion of false-positive diagnoses.

Previous studies have shown that 10% of patientswith GDM would remain undiagnosed if a threshold of140 mg/dL is adopted for the glucose challenge test, andnearly all cases of GDM would be detected if a thresh-old of 130 mg/dL is used.7 Although it is not clearwhether women with gestational diabetes with screeningtest values between 130 and 139 mg/dL have the samerate of complications than patients with higher screeningvalues, an increased risk of maternal hyperglycemia, ne-onatal hypoglycemia, and macrosomia has already beendocumented in this group.7 Also, recent studies haveshown a significant increase in perinatal morbidity inuntreated patients with GDM, including when a thresh-old of 130 mg/dL was used for a positive glucose chal-lenge test.11,12 Our study shows a similar incidence of10.7% of GDM in the screening group of 130-139-mg/dL and further supports using a threshold of 130 mg/dL for obtaining a GTT.

In conclusion, our data pertaining to pregnant blackwomen support the use of 130 mg/dL as the thresholdfor a positive glucose challenge test and suggest the useof a GTT to confirm the diagnosis of GDM forscreening values up to 200 mg/dL.

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