The two most dominate reasons for a neonate’s low birth weight are prematurity and intrauterine growth retardation (IUGR) (Fig. 50.1). Premature neonates are born before 37 completed weeks of pregnancy and the term prematurity is used regardless of birth weight. Neonates who are small for gestational age (SFGA) weigh less at birth than would be predicted for their gestational age. This group usually includes neonates born below the 10th centile. As these two groups of neonates are likely to present with a range of problems requiring specialist intervention, practitioners must be capable of assessing them at birth and identifying and managing problems which are present. Ongoing vigilance is needed in recognising new problems which evolve in the first few days or even weeks of life. Specialist knowledge, clinical expertise and vigilance are crucial in providing optimal care.

One of the tools commonly used in assessing such neonates is centile charts (Fig. 50.2) which help to define the small-for-gestational-age neonates by using their birth weight which is invariably more than two standard deviations below the mean or less than the 10th percentile of a population-specific birth weight for gestational age. Whilst variations in fetal growth exist, birth weight is frequently used to distinguish between neonates who are small for gestational age from those who are small but normal for gestational age. Assessments of fetal growth, development and maturation must take into consideration variations in genetic and environmental factors which are known to impact on the expectant mother’s health as well as the growth of her fetus(es).

In most instances, assessment of fetal growth would be based on the length of gestation by taking into account the onset of the last menstrual period, the size and shape of the growing uterus and maternofetal hormone profile. Ultrasonic studies, and in some instances, amniocentesis, provide additional information when required. Most fetuses fall into a symmetric or asymmetric growth pattern. Symmetric growth implies that both brain and body growths are limited, whereas asymmetric growth implies that body growth is restricted to a greater extent than head and brain growth. The mechanisms for such asynchronous growth are not understood although Anderson & Hay (1999) suggest that increased cerebral blood flow relative to the remainder of the systemic circulation may contribute. The birth of low-birth-weight neonates generally warrants the presence of experienced paediatricians at the delivery.

In addition to establishing the birth weight, length, head circumference and gestational age, all small neonates must undergo a thorough physical assessment that may include scoring of neurological and neuromuscular capabilities initially devised by Dubowitz et al (1970) but used widely in the United Kingdom (Fig. 50.3). However, as this scale awards points for neurological states as well as external criteria, it is not always suitable for assessing the gestational age of sick neonates. The Parkin score (Parkin et al 1976), which uses exclusively external criteria, is quicker to use, though less accurate (Fig. 50.4). However, assessments may have adverse effects on the stability of the neonate’s condition. They are less useful with the more sophisticated fetal assessments using ultrasound, unless the mother is seen for the first time in labour (England 2003).

Although preterm births occur spontaneously, in many circumstances the sequence of events may be medically controlled for maternal or fetal safety. Whilst 40% of such births have no established causes, a range of contributing factors such as physical disorders in the fetus or the mother, or the mother’s social class, may play a key role (Table 50.1). This is not surprising as many suboptimal health problems appear to be the consequence of interplays between genetic and environmental factors (see Ch. 8 and Ch. 15).

Proactive care of the premature neonate aims at supporting the physiological shortfalls which are apparent at birth. Usually this care is initiated before or during labour to ensure the neonate’s survival. Ideally all premature neonates should be delivered in maternity departments with specialist neonatal care facilities as the transfer of such small neonates is fraught with problems and increased risks.