Baby drop from 25th percentile to 3rd in 2 weeks

I had a ultrasound at 33 36 and yesterday at 38 weeks. They always said he was small but in the normal range. 25th percentile. From the 36 to 38 week ultrasound he didn't change and said he dropped to the 3 to 5th percentile. They said that its best to take him out now while he's healthy. I have to go to my doc Wednesday and see what she says. Anyone else have this experience?