Introduction

Twenty years since the first publication of the concept of customised fetal growth charts,1 this may be an opportune time to reflect on its current and potential role in perinatal care.

The customised standard defines the individual fetal growth potential by three underlying principles. It is,

1. adjusted to reflect maternal constitutional variation;

2. optimised, by presenting a standard free from pathological factors such as diabetes and smoking; and

3. based on fetal weight curves derived from normal pregnancies, rather than neonatal weight curves which include pathological preterm deliveries.

Thus the standard strives to predict the weight to be reached in an uncomplicated pregnancy, and to detect if it has deviated from the norm due to pathological influences. In practice, software calculates a ‘term optimal weight’ (TOW) adjusted for maternal characteristics such as height, weight, ethnic group and parity, as well as the baby's sex if known. TOW is combined with a standard ‘proportionality’ function2 using Hadlock's fetal weight distribution3 to provide a gestation-related optimal weight (GROW) curve4 (http://www.gestation.net) (figure 1).