A random glucose test is just that. They measure your blood glucose
at just any time when you're eating
normal meals. This does not qualify as a screening for Gestational Diabetes. Depending on how long after your last meal and what you ate, the results could be normal, even if your blood sugar is not.
For a random glucose test to be any use at all, make sure that you eat a regular full meal 2 hours before the time that you will have the blood draw.