Surviving the first few days of life: Incidence and causes of sudden unexpected neonatal death or collapse, and potential prevention strategies

Background Sudden unexpected collapse in apparently healthy term newborn infants is rare but can result in death or severe morbidity. The incidence of Sudden Unexpected Postnatal Collapse (SUPC) varies throughout the world at 0.026–1.3 per 1000 live births. This incidence is likely underestimated due to inconsistent reporting, differences in classification, and reporting only being mandatory for fatal SUPC. Previous large-scale national-level research indicates that the aetiology of collapse or death is unidentified in the majority of cases. In Australia, there is an absence of data, particularly population-based data, on these rare events. Prevention strategies such as early saturation screening or evaluation of growth or body composition are not possible if there is no data identifying potential SUPC risk factors. Aims This thesis has three main aims. 1) To determine the incidence, risk factors, aetiology and short-term outcomes of sudden unexplained death or collapse in apparently healthy term infants in Australia. 2) To determine the incidence and aetiology of babies identified as having neonatal hypoxaemia according to early saturation screening within six hours of life, and whether such early recognition can prevent SUPC. 3) To demonstrate that infants with poor growth and nutrition are at greater risk of morbidity secondary to hypoglycaemia, and that measures of body fat better identify such infants than birth weight percentiles alone. Methods This thesis is based on a national surveillance case study, three prospective hospital-based cohort studies, and a prospective survey. The national surveillance study was conducted through the Australian Paediatric Surveillance Unit (APSU) to look at the prevalence, risk factors and aetiology of sudden unexplained death or collapse in apparently healthy term babies within the first seven days of life. A hospital-based cohort study was performed that explores the use of saturation screening (within 6 hours of life) to identify neonatal hypoxaemia, which could possibly prevent SUPC. Recognising that the newborn period is a vulnerable time for babies, in a retrospective audit, we examine how low %BF, which indicates poor neonatal nutritional status, is a risk factor for hypoglycaemia and neonatal morbidity. To define low body fat more accurately, 7667 babies underwent body fat assessment as part of a hospital-based cohort study. The results were used to construct gender- and gestation-specific body fat percentile charts. We also completed a prospective survey of screening practices in neonatal intensive care and special care units throughout Australia and New Zealand. Results Cardiorespiratory adaptation was found to be important and we demonstrate that poor/delayed adaptation is the leading cause of sudden unexpected neonatal death or collapse in approximately one in five cases in Australia. Some 56% of reported cases died and 44% survived, with 19% of survivors being neurologically abnormal on discharge. The most common causes of a failed saturation screening are delayed transition to extra-uterine life and respiratory disease. Infants born by elective caesarean section are more likely to have saturations < 95% upon early screening. Furthermore, we demonstrate that infants with poor growth are at potentially greater risk of morbidity secondary to hypoglycaemia and that measures of body fat identify these infants better than birthweight centiles alone. Conclusion Our findings add to the increasing literature on SUPC in term infants, highlighting that the causes are often identifiable and preventable, and their mortality rates high. We also raise concerns that the Australian Surveillance System is focused on paediatric rather than neonatal disease. In addition, we present information that can be used to inform potential prevention and screening strategies for healthy term newborn infants. Early saturation screening and determination of body composition in the early newborn period can identify babies at risk of SUPC and provide opportunity for prevention. Babies found to have low %BF should be screened for morbidities such as neonatal hypoglycaemia. Finally, screening practices at neonatal units in New Zealand and Australia lack consistency which potentially affects the identification of the at-risk infant