Hi

My wife is pregnent(32 weeks), in scan they have mentioned that kidney size is different when compared to right and left.

Like(3 in right and 1.5 in left approx)

Will it be serious issue. Doctor said one kidney is normal and another is small

Please advice what is the reason and what can de done to rectify it.

You should be asking the doctor this question. We don't know, nor are privy to your wife's medical history.