BPP Ultrasound

I had an ultrasound at 32 weeks and it said baby was around 5.5 lbs. Doctor has since them been measuring my belly height (forgot the correct terminology for this) and it’s always larger than what he says it should be. This past Friday I went in and he said with my weight gain being more than it should and the fact that my baby is measuring big, he wants to do a BPP next Friday for precaution. He just described it as an ultrasound but has anyone had this before? I’m kind of nervous about what it will mean if baby is measuring big.