My wife anomaly scan showed placenta grade 2 maturity as my wife is 20 week pregnant.is there anything to worry or it is normal?

It's normal: Placentas are usually graded on sonogram base on the degree of calcification that is present within the placenta. These may appears as white echogenic areas on sonogram. The grading as somewhat subjective but in general the farther along the pregnancy, the more mature is the placenta and hence there is more calcification present. A grade 3 placenta may imply that the pregnancy is term or near term