A line drawing showing the measurements made on the ultrasound images in figs 2-5 (A–D, respectively), with arrows indicating the correct caliper position and alignment. A line drawing showing the measurements made on the ultrasound images in figs 2-5 (A–D, respectively), with arrows indicating the correct caliper position and alignment. M W Davies et al. Arch Dis Child Fetal Neonatal Ed 2000;82:F218-F223 Copyright © BMJ Publishing Group Ltd & Royal College of Paediatrics and Child Health. All rights reserved.