Introduction Stillbirth and fetal growth restriction are associated with lower placental weights compared to live, appropriately grown infants. Sonographic measures of placental size have been used to predict later pregnancy complications but have not been related back to true placental size. We aimed to validate measures of placental size in the third trimester of pregnancy.

Methods Ultrasonographic placental examination was performed in 30 singleton pregnancies of 35–42 weeks’ gestation within seven days of delivery. Placental length, width and depth were measured using two-dimensional (2D) ultrasound, placental volume was estimated by a novel elliptical model, Kliman placental gas gauge and two three-dimensional (3D) ultrasound techniques (rotational (VOCAL) and slicing methods). Following delivery, the placenta was measured, weighed and volume determined. Sonographic and true placental measures were compared using linear regression.

Results Elliptical (but not Kliman placental gas gauge) 2D and all 3D ultrasound estimates of placental volume each related significantly with true placental volume with similar accuracy (Table 1) but not to placental weight (p > 0.05). VOCAL demonstrated higher accuracy than the elliptical model at the smallest placental volumes.

Conclusion True placental volume can be accurately predicted using 2D and 3D ultrasound in the third trimester. 3D ultrasound may improve detection of the abnormally small placenta. Further research is required to establish whether this measurement can predict poor pregnancy outcomes related to placental disease.