Fasting glucose test at 40 weeks?

So I got a call from my Dr office today saying that my Dr would like me to come in before my appt. On Wednesday to do a fasting glucose test. Which would consist of me coming in after 10 hours of not eating having my blood drawn and then I would go home. No drinking any sugar drink or anything. I'm 40 weeks tomorrow and so confused as to why she would want me to do this. I had an ultrasound done last week and found out my baby is in the 90th percentile for size but big babies run in my family and I did a 3 hour glucose test at 28 weeks and everything came back totally normal. I can't imagine what info she could gain from me doing another blood draw especially if he is coming out in the next week.