Influence of the Time of Day and Fasting Duration on Glucose Level following a 1-Hour, 50-Gram Glucose Challenge Test in Pregnant Women

BACKGROUND Previous studies have shown that the time of day (TD) of glucose measurement and the fasting duration (FD) influence the glucose levels in adults. Few studies have examined the effects of the TD and FD on the glucose level following a 1-hour, 50-gram glucose challenge test (GCT) in pregnant women in screening for or diagnosing gestational diabetes mellitus (GDM). The objective of this study was to investigate the influence of the TD (morning, afternoon, night) and the FD (the time of the last food ingestion as follows: ≤1 hour, 1-2 hours, and >2 hours) by examining their combined effects on the glucose levels following a 50-gram GCT in pregnant women. METHODS AND RESULTS We analyzed the data of 1,454 non-diabetic pregnant Taiwanese women in a prospective study. Multiple linear regression and multiple logistic regression were used to estimate the relationships between the 9 TD-FD groups and the continuous and binary glucose levels (cut-off at 140 mg/dL) following a 50-gram GCT, after adjusting for maternal age, nulliparity, pre-pregnancy body mass index, and weight gain. Different TD and FD groups were associated with variable glucose responses to the 50-gram GCT, some of which were significant. The estimate coefficients (β) of the TD-FD groups "night, ≤1 hr" and "night, 1-2 hr" revealed significantly lower glucose concentrations [β (95% confidence interval [CI]): -6.46 (-12.53, -0.38) and -6.85 (-12.50, -1.20)] compared with the "morning, >2 hr" group. The TD-FD groups "afternoon, ≤1 hr" and "afternoon, 1-2 hr" showed significantly lower odds ratios (OR) of a positive GCT; the adjusted ORs (95% CI) were 0.54 (0.31-0.95) and 0.58 (0.35-0.96), respectively. CONCLUSIONS Our findings demonstrate the importance of standardizing the TD and FD for the 1-hour, 50-gram GCT. In screening for and diagnosing GDM, the TD and FD are modifiable factors that should be considered in clinical practice and epidemiological studies.