The purpose of any form of antenatal fetal surveillance must be to recognize accurately fetal and environmental conditions which adversely influence perinatal mortality and morbidity at an early enough stage to use whatever corrective measures may be available. At booking, risk assessment identifies the woman with social or medical predictors of poor pregnancy outcome from the woman in good health who should have a successful pregnancy. Thus the high-risk patient is a woman in whom the chances of an adverse outcome to herself and/or the baby are greater than the incidence of that outcome in the general obstetric population. The corollary of this definition however, is that the “low-risk” obstetric patient still has the chance of an adverse outcome but the incidence of that outcome is that of the general obstetric population. In the absence of information relating specifically to the fetus, this maternal data is then extrapolated to predict the high or low risk fetus. This system however, does not predict the high risk normally formed stillbirth who is often, but not always, smaller than the gestational age-matched liveborn infant but who is commonly delivered of the low risk woman.

The unstated aim of preterm fetal welfare surveillance is to enable the obstetrician to delay delivery if a fetus is not at risk of death or permanent damage. Although the penalty for preterm delivery has decreased with advances in neonatal care, the obstetric goals of prolonging pregnancy and minimizing intervention persist. The modern goal of minimizing costs also dictates appropriately timed delivery.

The term “dysmorphology” was coined by Dr David Smith in the 1960s to describe the study of human congenital malformations. Literally, it means “the study of abnormal form”, emphasizing a focus upon structural abnormalities in development.2 As a scientific discipline, dysmorphology combines concepts, knowledge and techniques from paediatrics, clinical genetics and embryology.

Among serious fetal anomalies currently detectable with ultrasound, defects of the central nervous system (CNS) are among the most common. These congenital anomalies are especially likely to burden not only affected children with severely limiting handicaps, but also their families with long-lasting anguish and financial responsibility. It is appropriate that interest in methods for improving prenatal detection of these abnormalities has intensified. Alphafetoprotein screening programmes are now widely available, and many papers have been written describing useful sonographic observations that enhance prenatal diagnosis. As a consequence, the majority of the most common serious neural axis defects including fetal hydrocephalus, anencephaly, myelomeningocele and encephalocele, previously detected almost exclusively at birth, today can be accurately detected prenatally. A few observations in the fetal brain and spine have proven to be especially useful in this task. This article presents a simplified and effective approach to the general sonographic survey of the neural axis in fetuses at average and increased risk for these anomalies. The aim is to improve not only accuracy of diagnosis of CNS malformations, but the efficiency and confidence of the examiner.