Objective: To assess the prevalence of GDM in GCT screened women at Maharaj Nakorn Chiang Mai Hospital.
Study design: Retrospective descriptive study.
Setting: Department of Obstetric and Gynecology, Maharaj Nakorn Chiang Mai Hospital.
Material and Method: One thousand pregnant women who attended the antenatal care clinic and delivered at Maharaj Nakorn Chiang Mai Hospital from October 2001 to December 2002 were recruited into the study. Glucose challenge test (GCT), 50-g glucose oral load with 1-hr plasma glucose measurement, was performed in GDM high-risk pregnancies. If GCT was positive, oral glucose tolerance test (OGTT), 100-g glucose orally, was done to confirm the final diagnosis. All relevant data including demographic information, previous obstetric history, risk factors for GDM, GCT and OGTT results and pregnancy outcomes were collected for further statistical analysis.
Main Outcome Measures: Prevalence of GDM in GCT screened women, obstetric complications and pregnancy
outcomes.
Results: There were totally 1,000 pregnancies enrolled into the study. Despite 451 pregnant women being eligible for GCT, only 411 cases were tested with 164 positive results. 29 cases of GDM were detected with the prevalence of 7.05%. (CI 95% = 0.048, 0.099). As a result, the sensitivity, specificity, positive predictive value, and negative predictive value of GCT were 100%, 64.66%, 17.68% and 0%, respectively. In the GDM group, the common indications for GCT screening were advanced maternal age (75.4%), familial diabetic history (22.1%) and glycosuria (6.8%). Furthermore, only 1 case of pregnancy-induced hypertension was found with cesarean section, preterm birth, LGA and SGA of 27.6%, 10.3%, 3.45% and 13.79%, respectively. There were 2 cases of pregestational diabetes mellitus (PGD; 0.2%) with 40 high-risk pregnancies (4%)
without screening.
Conclusion: The selective GCT screening strategy was highly effective and revealed 7.05% of GDM prevalence.
Its impact on obstetric complication and pregnancy outcome was inconclusive due to the small number of studied population. Careful history reviewing plays an important role in identifying GDM risk factor for GCT screening.

Keywords: Gestational diabetes mellitus (GDM), Prevalence of GDM, Glucose challenge test (GCT), Oral glucose tolerance test (OGTT), Selective screening strategy