36w ultrasound - placenta degrading

Had my 36w ultrasound today and they said that baby is 5lb8oz. I think he's about in the 40th percentile. But his abdomen is in the 2 percentile. They said the placenta is starting to degrade and baby isn't getting everything he needs to grow correctly. 
The ultrasound dr said they are having me back next week (7 days) to check and see if further degradation has occurred but not doing anything right now. 
Seems odd that if baby isn't growing correctly they are waiting an entire week??
I see my regular ob dr tomorrow. Anyone else have this? What did they do?