December 15, 2005
Question from New Jersey, USA:
I had taken the one hour screen at 28 weeks, five days pregnant. I fasted that morning but, the night before, ate half of a whipped cream cake. My result was 141 mg/dl [7.8 mmol/L], with lab cutoff of 140 mg/dl [7.8 mmol/L]. The doctor said I should do a three hour test as a precaution. What is the likelihood that I will fail a three hour and have gestational diabetes? Did that half cake 12 hours before have any bearing?
In theory, you do not have to be fasting to take the one hour glucose test, but the results may be more predictive following a fast. Despite the sugar load the night before, your result is only slightly elevated. If it was truly 12 hours since you ate, then that is sufficient fasting. My personal preference is to use 135 mg/dl [7.5 mmol/L] as a cutoff. Nevertheless, there is a good chance that your three hour test will be normal although I cannot promise anything. For the three hour test, you absolutely have to fast, otherwise the results will be invalid.