AFI 20cms at 37 weeks. is it normal?

Am 37 weeks pregnant and underwent growth scan yesterday. It says that my AFI is 20cms and is mentioned as polyhydromnios. Currently my baby's weight is 2.8kgs and my glucose tolerance tests shows normal. I don't have any thyroid problems too. Tiffa scan was also done during my 6th month and no abnormalities have been detected. As per the internal examination done by the doctor it was told that my baby is correctly positioned- head down cephalic presentation. Doctor had advised me to go for normal delivery in the next week itself. What is the ideal levels of AFI at this stage? Is it dangerous if I don't deliver the baby by next week? Is there a possibility for me to wait for some more days to deliver? If yes, how many more days can I wait? What are the complications in polyhydromnios? Please advice