How normal is 'normal'? validation of normal 75g OGTT results by neonatal outcomes

Headnote

Keywords: Gestational diabetes mellitus, glucose tolerance test, neonatal outcome

[OP-070]

Objective: The study was performed to investigate the impact of different 75g OGTT (oral glucose tolerance test) target ranges within normal limits on neonatal outcomes and thereby to determine the validity of 75g OGTT thresholds.

Material and Methods: For this observational study, 110 pregnant women, at 24-28 weeks of gestation, who attended our outpatient antenatal clinic and diagnosed to have no GDM (gestational diabetes mellitus) by using 75g OGTT were enrolled after obtaining written informed consent from all participants. The diagnosis of the GDM was made according to the IADPSG/ADA (International Association of the Diabetes and Pregnancy Study Groups/ American Diabetes Association) criteria, when any of the following plasma glucose values are exceeded: fasting >= 92 mg/dl, 1h: >= 180 mg/dl, 2h: 153 mg/dl. The exclusion criteria included women with GDM, pre-gestational DM, hypertension, multiple pregnancies and fetal anomalies.

The normal 1-hour and 2-hour ranges of 75 gr OGTT were further divided into four different sub-groups; for the 1-hour as group 1 (< 120 mg/ dl), group 2 (120-139 mg/dl), group 3 (140-159 mg/dl) and group 4 (160180 mg/dl) and for the 2-hour as group 1 (< 120 mg/dl), group 2 (120-134 mg/dl), group 3 (135-149 mg/dl) and group 4 (150-153mg/dl). Neonatal outcomes were compared between these new range groups. All data were analyzed using Statistical Package for Social Sciences (SPSS) for Windows, Version 22 (IBM Corp, Armonk, NY) and p values <0.05 were considered to be statistically significant. Continuous variables are presented as mean±SD and categorical variables as numbers and percentages. For the analysis of qualitative data, chi-square test was used. For the analysis of quantitative data, one-way ANOVA (posthoc Tukey) and Kruskal Wallis tests were used.

Results: The number and percentage of the subjects were 50 (45.5 %), 32(29.1%), 18 (16.4%) and 10 (9.1) for the first hour and 82 (74.5 %), 14 (12.7%), 10 (9.1 %), and 4 (3.6%) for the second hour, for groups 1-4, respectively.

For the 1 hour results, there was no statistically significant difference between groups in terms of neonatal hypoglycemia, hyperbilirubinemia, intensive care unit admission, birth weight, abnormal result and LGA (large for gestational age) rates; however, the rate of SGA (small for gestational age) infants was statistically significantly higher in group 2 compared to those in groups 3 and 4. As for the 2 hour statistically similar results were found between the groups ( p> 0.05).

Conclusion: In conclusion, this study demonstrates 75g OGTT (IADPSG/ ADA) has reliable threshold values for GDM screening as the neonatal outcomes do not differ between the low normal and high normal levels of the first and second hour test results and provides evidence that there are still adverse neonatal outcomes in women with OGTT results below the current thresholds and the study also reports a higher number of SGA in the glucose range 120-139 mg/dl of the first hour which needs further evaluation. As a result, the validity of the 75g OGTT thresholds still needs to be investigated and verification by large studies is needed.