I got it at 35 weeks. It sort of depends really on how long you have had it. At this late stage I think they will just scan you to see whether they think baby is big and whether you are carrying a lot of fluid then depending on the results consider whether they might want to induce you a bit early. They will also tell you to keep a check on your blood sugars until the baby comes.
Main thing now is don't worry - there's no need to be worried at this late stage - and don't be pushed into anything. I was induced last week because they thought my baby was huge. He wasn't and the induction was unnecessary. I don't believe he was affected at all. They also made a great fuss before hand about monitoring his blood sugar when he came out and how he might need to go to a special care baby unit. There wasn't a word said about any of this when he was born - oh and he wasn't even that big.
I suggest you find out tomorrow what the result is then come back on here and chat to the ladies on the GD thread. they talk a lot of sense.