Use of Oral Glucose Tolerance Test and Glycated Haemoglobin at 20 Weeks of Gestation or Less to Predict or Exclude Subsequent Development of Gestational Diabetes Mellitus in the Current Pregnancy in High-risk Patients Abstract

Helena HL LEE, Kandice Ellen LI, Kwok-Yin LEUNG

Objective:
To determine cutoff values of oral glucose tolerance test (OGTT) and/or glycated haemoglobin at ≤20 weeks of gestation that could predict or exclude subsequent development of gestational diabetes mellitus (GDM) in the current pregnancy in high-risk patients.

Methods:
Retrospective review of all non-diabetic pregnant women who had undertaken 75 g OGTT at ≤20 weeks of gestation in Queen Elizabeth Hospital, Hong Kong, from 1 April 2011 to 30 September 2011, was performed. Gestational diabetes mellitus was diagnosed in accordance with the 1999 World Health Organization criteria. If early OGTT results were normal, second OGTT was performed at 24 to 30 weeks. Sensitivity, specificity, positive predictive value, negative predictive value of the cutoff values, and proportion of OGTTs that could be spared at 24 to 30 weeks of gestation were calculated.

Results:
In all, 58 (26%) pregnant women were diagnosed to have GDM by the first OGTT; 45 (30%) women with normal first OGTT had GDM diagnosed by the second OGTT, with higher mean 2-hour plasma glucose level than those in the non-GDM group (p<0.05). The best cutoff value that excluded GDM was 2-hour plasma glucose level of <4.4 mmol/L, which spared 5.3% of second OGTTs. The sensitivity, specificity, positive predictive value, and negative predictive value were 100%, 92.8%, 32.3% and 100%, respectively.

Conclusion:
Approximately 5.3% of OGTTs at 24 to 30 weeks of gestation among women with multiple risk factors for GDM may be omitted using a 2-hour plasma glucose cutoff value of <4.4 mmol/L in early pregnancy, provided that there is no onset of new risk factor(s) after the first OGTT.

Hong Kong J Gynaecol Obstet Midwifery 2015; 15(1):29–38

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