Preterm birth is defined as ‘any neonate whose birth occurs before the thirty seventh week of gestation’1 and represents approximately eight percent of all pregnancies1-4. It is eminent that these preterm infants are at risk of physical and neurological delay, with prolonged hospitalisation and an increased risk of long-term morbidity evident in prior literature3, 5-13. Innovative healthcare over the past thirty years has reduced mortality significantly14, with the survival rate of preterm infants having increased from twenty five percent in 1980 to seventy three percent in 200715. Despite, this drop in mortality long-term morbidity continues to remain within these surviving infants ...view middle of the document...
Gestational age is a continuum from conception to birth, with each week improving fetal neurological outcome4, 17, 18. In earlier years prematurity relied solely on birthweight for identification, defining prematurity as ‘any infant born below 2500g’1, 16. However, this resulted in misclassification of infants as heterogeneity in particular ethnicity caused preterm infants to be classified as full term when in fact they were preterm1. Upon this realisation, it was evident that birthweight was dependent of gestational age and thus the creation of birthweight percentile was formed. Birthweight percentile uses the relationship between gestational age and birthweight to classify infants into three percentile groups of neonatal risk1. Large for gestational age (LGA) which accounts for infants that exceed the 90th percentile, small for gestational age (SGA) which depicts infants born below the 10th percentile and appropriate for gestational age (AGA), between the 10th- 90th percentile which represents healthy birthweight for gestational age (Refer to figure 1). This classification system standardises for heterogeneous factors e.g. gender, ethnicity along with maternal factors to ensure individuality does not heavily influence neonatal risk1.
Figure 1: classification of newborns by birth weight and gestational age1
It is well established that SGA infants possess the highest risk of neonatal complications, with gestational age inversely related to increased mortality6, 16. It is further noted that normal fetal trajectory and brain growth is some degree neuroprotective19, 20. What is overlooked by literature is the implications of being LGA and whether infants born preterm but large birthweight possess inverse outcomes to SGA. If SGA undoubtedly leads to poor neural outcomes, and normal growth is deemed somewhat neuroprotective. Is there a difference between appropriate growth and LGA? And is this difference inversely proportional to the observations of SGA?
2 .0 Causes and Risk factors for Preterm Birth
In recent decades literature has validated several causes of preterm birth, with a minority of cases idiopathic. Prematurity is typically a result of maternal or fetal risks6, 21 (refer to figure 2). These risk factors increase the likelihood of early delivery and consequently increase the likelihood of long term physical and neurological impairment.
Figure 2: Causes and risk factors leading to preterm birth6, 21: 1 – a bacterial infection of fetal membrane and amniotic fluid
On occasion, preterm birth is induced by physicians as a result of recognised fetal problems such as In utero growth restriction (IUGR). IUGR is a complex condition with aetiology poorly understood. The foetus may be small as a result of multiple birth or due to placental insufficiency and inadequate fetal gas exchange4, 18, 22, 23. IUGR infants are frequently delivered early without actually achieving the weight bracket that would define them as SGA. For this reason, the...