Aging placenta

I'm 34 weeks and today my ultrasound showed my placenta is "aging" at a faster rate than it should and has some calcification. Baby boy isn't growing as fast as they would like either. He's almost 4 lbs. I go back for another ultrasound next week for them to decide if it's safe for him to stay or if they need to go ahead and take him. From what the dr said and what I've read I'm nervous for him to stay but I know he needs to gain weight if possible. Anyone ever dealt with this? I'm not a smoker. I read smoking can be a factor in this for some.