Placental grading on ultrasound is based on following criteria:-

Placental grading (Grannum classification)refers to an ultrasound grading system of the placenta based on its maturity. It primarily affects the extent of calcifications. Factors evaluated include placental calcium deposits and chorionic plate undulations. GRADE FEATURES Grade 0 <18 weeks uniform echogenicity smooth chorionic plate Grade I 18-29 weeks Scattered echogenicities and subtle chorionic plate undulations Grade II 30-38 weeks Echogenic stippling at the basal plate Grade III >= 39 weeks Echogenic indentations extending from the chorionic plate to the basal plate which resemble cotyledons.