One of the reasons my ob induced with my first was because he was measuring behind and she was as afraid my placenta was weakening and not going to hold up to full term. Could be a possibility, ask you ob at your next appointment just for peace of mind.
If you were measuring a week ahead at 32 weeks that would mean at one point your baby measured at 33 weeks, and now its measuring 30? that means your babies shrunk??
I've heard of that happening, sometimes that's just how the baby is gaining weight. My doc said its normal if that happens tho. Maybe your baby is smaller?