Lowest threshold values for the 75g oral glucose tolerance test in pregnancy

Abstract

Introduction: A previous study has suggested that with increasing oGTT thresholds there was a statistically increasing risk of maternal and foetal morbidity in the form of hypertensive disorders complicating pregnancy and macrosomia. The present study aims to identify whether this gradient risk is extant with lower blood glucose levels. Methodology: A total of 1289 75-gm oGTTs were performed during pregnancy. These were divided according to their fasting and 2-hour values into categories: A. Fasting values <=4.5 mmol/l (n=316), 4.6-5.5 mmol/l (n=681), and >=5.6 mmol/l (n=292); and 2-hour values <=6.5 mmol/l (n=453), 6.6-8.5 mmol/l (n=433), 8.6-9.5 mmol/l (n=176), and >=9.6 mmol/l (n=208). The incidence of hypertensive disease during pregnancy, the macrosomia rate, and the mean birth weight were assessed in each group. Results: The data confirm that a significant rise in the incidence of hypertensive disease occurs at a fasting vlood glucose value of >=5.6 mmol/l, while the macrosomia rate rises after >=4.6 mmol/l. The mean birth weight increased progressively with increasing fasting blood glucose thresholds. There is furthermore a progressive rise in the incidence of hypertension noted with significance being reached at a 2-hour blood glucose value greater than 9.6 mmol/l. However no such relationship appears to be present for the incidence of macrosomia; and there was no significant differences in mean birth weights with increasing 2-hour post-load glucose values. Conclusions: The study suggests that fasting blood glucose values may be a better indicator of maternal and foetal adverse risk outcomes with increased adverse foetal outcomes being indicated at levels >=4.6 mmol/l. The 2-hour post-75g oGTT values appear to be useful as adverse risk indicators only at levels >-9.6 mmol/l.