Measurement of placental volume with real-time ultrasound in mid-pregnancy

A new method to measure placental volume in mid-pregnancy using real-time ultrasound is described. The method is an adaptation of the B-mode parallel planimetric technique. The mean error of in vitro measurements on 45 balloons (mean volume 186 mL range: 88-485 mL) was -2.24 mL, standard deviation 6.76 mL. The error standard deviation of in vivo placental volume measurements was 16.4 mL (volume range: 173-396.5 mL). Placental measurements were made on 175 women between 14.3 weeks and 21.4 weeks, menstrual age (MA) and a smooth centile curve derived. Median volume increased linearly from 144 to 329 mL. The size of the ultrasound probe limits the technique to use before 20 weeks, MA.