Comparison of one step 75 g glucose tolerance test and two step 50g-100g glucose tolerance test in gestational diabetes screening and determination of their correlation with postpartum glucose tolerance test

In this randomized prospective study, 857 pregnant woman admitted to the Akdeniz University, Medicine Faculty Hospital were tested with GDM screening between January and December 2014. In our study, we have 100 patients. 50 of them were diagnosed with 75 g OGTT, and other 50 were diagnosed with 50 g - 100 g OGTT (11 of them were diagnosed with two step test by other healthcare centers and then followed by our clinic) at the 24 - 28th week of gestational weeks. In present study, we aimed to compare the adverse pregnancy outcomes and postpartum abnormal glucose results of patients who were diagnosed with GDM using one step 75 g OGTT or 50 g-100 g OGTT by doing 75 g OGTT at postpartum sixth week. There were no significant differences among groups about maternal characteristics such as gravidity, parity, height, weight, BMI and age. There were no differences about fetal birth weight, gestational age and birth patterns. There were also no statistically significant differences among groups about macrosomia, preeclampsia and preterm birth which are all adverse pregnancy outcomes of GDM. For the chosen treatment options (only diet or insulin), there were no statistically significant differences among groups. The mean gestational week for HbA1c analysis was 28.5 for the group diagnosed with 75 g OGTT and 30 for the group diagnosed with 50 g - 100 g OGTT. The differences among groups for the mean week in which HbA1c control is done was found to be statistically significant (p<0,0009) and it was interpreted in this way, in the two step test only persons who exceed the threshold level were subjected to the diagnostic test. The average HbA1c level in pregnancy was higher in the 75 g OGTT group, than the 50 g-100 g OGTT group and the difference was statistically significant. There was also no statistically significant difference between groups for the number of women who diagnosed with impaired fasting glucose, impaired glucose tolerance and diabetes by using postpartum 75 g OGTT and WHO criteria. Patients diagnosed with impaired fasting glucose, impaired glucose tolerance and diabetes were classified as abnormal postpartum glucose group. The rate of abnormal postpartum glucose groups in one step 75 g glucose tolerance test and two step 50 g-100 g glucose tolerance test were 18% and 20%, respectively. In this abnormal postpartum glucose group, pregnancy HbA1c levels in pregnancy was found to be significantly higher (p<0,0009). In both groups, two subgroups were created; one includes patients with abnormal postpartum glucose and the other includes persons with normal postpartum glucose according to the WHO criteria. HbA1c levels in pregnancy were statistically significantly higher in the abnormal postpartum glucose group for both 75 g OGTT and 50 g - 100 g OGTT groups. Correlation between higher HbA1c and abnormal postpartum glucose levels was still present when all the women evaluated together. In our study, we failed to find significant differences about adverse pregnancy outcomes and postpartum results between GDM screening tests. Therefore, we can not highlight that any test is superior to the other. In this study, it is showed that patients with abnormal postpartum glucose levels had higher HbA1c levels in their pregnancy period. Consequently, in patient with gestational diabetes who diagnosed by GDM screening test, HbA1c level may be suggestive for the postpartum abnormal glucose level of the patient.