Placental weight, digitally derived placental dimensions at term and their relationship to birth weight.

Objective. A few recent studies have investigated the relationship between birth weight and digitally derived placental dimensions, and no standardised methodology has been used. The aims of this study are to compare manually derived placental measurements with those derived digitally and to establish the relationship of birth weight to the placental weight and circumference. Methods. Three hundred fifty-one consecutive unselected women with singleton pregnancy delivering in a tertiary maternity unit at 37-42 weeks were recruited. Manual and digital placental axis measurements (using calibrated digital imaging and 'Image J' software) were obtained and the circumference derived. The relationship between the two methods was assessed using a Bland-Altman plot analysed. The relationship between z-scores of birth weight, placental weight and placental circumference was investigated. Results. Manually and digitally obtained placental long axis, short axis and circumference measurements show close correlation (r = 0.70, 0.70 and 0.83, respectively). The z score of birth weight is significantly correlated with the z score of placental weight (r = 0.59, p < 0.001) and z score placental digital circumference (r = 0.40, p < 0.001). Birth weight: placental weight ratio is 7.20 and birth weight: placental circumference = 64.57 g/cm. Conclusion. There is close though not perfect agreement between the manual and digital placental measurements. Birth weight is strongly correlated with placental weight and circumference at term.