An amniocentesses always has a risk of miscarraige. If it is necessary for you to have than I would. If you really think about it everything has a risk. I would ask your doctor to weigh out the pros and cons before making your decision.
i had the same problem but i was around 20 weeks. i had "low amniotic fluid" and the amnio proved everything was fine. im not sure that 36 weeks is smart to do it at, but they use ultrasound to guide the needle and chances of anything bad happening are like 1%. at your gestational age, miscarriage chance is extremely low, the other risks are infection which chances are also low and possibly poking the baby but the ultrasound again will guide them. it only takes about 5-10 min and it's over. GL
They said that my baby was 9 lbs and wanted to see if his lungs were ready at 37 week. 5 mins after leaving the doctors I went into laber. So make sure that you have someone with you. I went to the hospital and they stopped it until we found out if his lungs were ready. By the way they were not.