Alternative methods of diagnosing gestational diabetes mellitus,☆☆

Presented at the Nineteenth Annual Meeting of the Society for Maternal-Fetal Medicine, San Francisco, California, January 18-23, 1999.
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Abstract

Objective: In an attempt to find more efficacious alternatives for the diagnosis of gestational diabetes mellitus, we evaluated whether (1) there is a glucose loading test value above which all glucose tolerance test results are positive, (2) omission of the third-hour plasma glucose measurement of the glucose tolerance test alters the sensitivity of the test, and (3) the presence of a fasting plasma glucose concentration ≥105 mg/dL suffices as a diagnostic standard after an abnormal glucose loading test result. Study Design: The charts of 512 patients who underwent 3-hour glucose tolerance tests at our institution between January 1995 and December 1996 were reviewed. Only subjects for whom the glucose loading test yielded plasma glucose levels ≥140 mg/dL were selected. The positive predictive value of a glucose loading test result ≥185 mg/dL was calculated. Results of glucose tolerance tests of subjects with elevated fasting plasma glucose concentrations were then evaluated to determine the positive predictive value for gestational diabetes mellitus of an elevated fasting plasma glucose concentration. Results: Among the subjects who underwent glucose tolerance tests, 22% (114/512) met positive test criteria for gestational diabetes mellitus. The positive predictive value for a glucose loading test result ≥185 mg/dL was 57% (25/44), whereas a glucose loading test result >199 mg/dL showed a positive predictive value of 69% (4/13). Omission of the third-hour glucose tolerance test value yielded a sensitivity of 87% (99/114). Among the 24 women with fasting plasma glucose concentrations ≥105 mg/dL, 96% had positive glucose tolerance test results. An elevated fasting plasma glucose concentration was highly associated with gestational diabetes mellitus necessitating insulin therapy (65%). Conclusion: An elevated glucose loading test result was associated with but not highly predictive of gestational diabetes mellitus. Omission of the 3-hour glucose tolerance test measurement resulted in failure to diagnose 13% of gestational diabetes mellitus cases. A fasting plasma glucose concentration ≥105 mg/dL was highly predictive of an abnormal glucose tolerance test result among patients with an elevated glucose loading test value. (Am J Obstet Gynecol 1999;181:1158-61.)

Section snippets

Material and methods

We identified from computer files the cohort of all pregnant women who had a 3-hour GTT performed at Brigham and Women’s Hospital between January 1995 and December 1996. This study group was “preselected”; all had undergone a screening glucose loading test in which the measured plasma glucose concentration was ≥140 mg/dL. During this period the hospital practiced universal screening, as recommended by the American Diabetic Association at that time.

A positive GTT result was defined as ≥2 values

Results

We reviewed the data for all 512 women who underwent GTTs during the study period. The population characteristics are shown in Table I, demonstrating that our study group consisted predominantly of women who were nulliparous, white, and ≥30 years old.

. Characteristics of women with positive glucose loading test results (n = 512)

Empty Cell%
Age at time of GTT
 <25 y11
 25-29 y20
 30-34 y35
 ≥35 y34
Race
 Asian11
 Black8
 Hispanic19
 White54
 Other4
 Unknown4
Parity
 Nulliparous43
 Primiparous22
 Multiparous31
 Unknown4
There were 114

Comment

The screening and diagnostic algorithm for gestational diabetes first set forth by O’Sullivan and Mahan4 is resource intensive, time-consuming, and inconvenient for a patient. In our preselected population of 512 women who underwent GTTs, we found that omission of the 3-hour value for the GTT would result in failure to diagnose 13% of the cases of gestational diabetes mellitus. In addition, there was no glucose loading test value above which the GTT result was consistently positive. In

Acknowledgements

We thank Michael Greene, MD, for helpful discussions on past and present practice guidelines. We also thank Micheline Chu, MD, for her assistance with data collection.

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