How to construct ‘normal ranges’ for fetal variables

Abstract A method to estimate reference intervals which depend on gestational age is described. The approach is based on standard statistical techniques, so implementation should be straightforward with most statistical packages. The reference limits are defined by simple formulae which may be plotted as smooth curves. The method is illustrated with analyses of three real datasets arising from different aspects of fetal monitoring. Copyright © 1998 International Society of Ultrasound in Obstetrics and Gynecology