+3 urine with normal blood sugar

Anyone else experience this? My wife has had glucose in her urine for the past three appointments with normal blood sugar readings and today had a slightly high reading. She is going in for the hour test next week and then will do it again in three weeks, as scheduled. The midwife said she wasn't too worried because we had just eaten, but we're worried. It doesn't seem normal to have sugar in your urine and have a normal blood sugar. Anyone experience this? Any pointers for us?