Advances in mathematical models of fetal growth: implications for ultrasound practice

This editorial article reviews some of the mathematical foundations which form the basis of ultrasound screening for fetal growth anomalies and the estimation of gestational age in the first trimester. Recent developments are discussed including individually fitted crown rump length (CRL) curves, customized antenatal growth charts, fetal growth velocity, and computer simulation for fetal growth screening. There is considerable scope for research on improving current clinical practices, as the detection rate for the small for gestational age (SGA) fetus remains at around 50% even in the best units. Accurate mathematical modelling of fetal growth is a critical aspect in developing clinically useful obstetric ultrasound services. The two main applications are in estimating gestational age and in monitoring fetal growth. The norms for commonly measured ultrasound parameters such as the CRL, fetal abdominal circumference (FAC), femur length (FL) and biparietal diameter (BPD) are well established, yet relatively few studies specifically address the issue of intrauterine weight gain. This is partly because for the purposes of growth monitoring, many ultrasound departments plot the individual measurements rather than weight estimates. However, several studies suggest that the estimated fetal weight (EFW) is at least as good as the FAC for the detection of the SGA fetus.1,2 In this paper we discuss advances in the mathematical modelling of fetal growth and their relevance to ultrasoundbased clinical practice.