Background The Grannum grading system (established in 1979) grades normal placentas from 0-III on their ultrasonic appearance. Little attention has been paid to the appearance on MRI. Adapting Grannum grade so that it can be used for MRI could help differentiate normal features from pathology.

Aim To determine the usefulness of Grannum grade in the MRI of normal placentas.

Method 200 fetal MRI scans were reviewed retrospectively and graded according to their Grannum grade features1 2 on standard fetal MR sequences.

Results Of the 200 MRI scans assessed 63% were from women in their 2^nd trimester and 37% from women in their 3^rd trimester. The mean GA was 172 days (range: 126-252 days). The MRI Grannum grades are shown in the table. A Spearman correlation coefficient of 0.349 (P value < 0.001) was calculated between the MRI Grannum grade and gestational age.

Conclusion Previously it was suggested that grading based on Grannum grade is seen on MRI of the placenta and is potentially clinically useful. Our data challenges its usefulness which is in line with current ultrasound data and questions the value of Grannum grade in clinical practice. Technological developments may have increased the detail of MRI and ultrasound such that the grading of placentas proves difficult.