Identification of risk factors which contribute to the increased mortality rates of preterm infants, 24 to 28 weeks' gestation, born in non-tertiary hospitals in Victoria

© 2014 Dr. Rosemarie Anne BolandPublication included in thesis:Boland, R. A., Davis, P. G., Dawson, J. A. & Doyle, L. W. (2013). Predicting death or major neurodevelopmental disability in extremely preterm infants born in Australia. Archives of Disease in Childhood: Fetal and Neonatal Edition, 98(3), F201-F204. DOI: 10.1136/archdischild-2012-301628Extremely preterm infants born before 28 weeks’ gestation have better prospects for survival if they are “inborn” at a tertiary perinatal centre. Despite a well-organised system of perinatal care in Victoria, extremely preterm infants continue to be “outborn” in non-tertiary hospitals. AIM The aim of this PhD was to investigate maternal and obstetric risk factors associated with extremely preterm birth in non-tertiary hospitals, and maternal and infant risk factors associated with perinatal and infant mortality. METHODS The research comprised four components: 1) A survey investigating perinatal healthcare providers perceptions of survival and neurosensory outcome following birth at 24 and at 28 weeks’ gestation; 2) Validation of web-based tool developed in the USA to predict survival and neurosensory outcome for a contemporaneous cohort of infants 22-25 weeks’ gestation, born in Victoria; 3) A 20-year retrospective population-based cohort study of all births 22 to 31 weeks’ gestation in Victoria in 1990-2009, investigating maternal risk factors associated with outborn birth and maternal and infant risk factors associated with perinatal and infant mortality; 4) A two-year prospective study of outborn and inborn infants 22 to 31 weeks’ gestation, resuscitated at birth and admitted to a neonatal intensive care unit (NICU) in Victoria in 2010-2011. RESULTS The survey revealed that many perinatal healthcare providers from both non-tertiary and tertiary hospitals underestimated survival and overestimated the risk of major neurosensory disability for preterm infants born at 24 or at 28 weeks’ gestation. Outborn infants were perceived to have much poorer prospects for survival and higher rates of major disability than actual rates for infants born in Victoria. The web-based “outcome estimator” developed in the USA accurately predicted mortality in inborn infants, 22-25 weeks’ gestation born in Victoria. It was not so accurate for outborn infants and overestimated the risk of major neurosensory disability in all 22-25 week infants born in Victoria. In 1990-2009, there were 16,914 births 22-31 weeks’ gestation in Victoria. Twenty-one percent of these births were in non-tertiary hospitals. The proportion of extremely preterm births in non-tertiary hospitals did not decrease over time, reaching 23% in 2009. There were 13,763 livebirths, of which 14% were in non-tertiary hospitals. There was a significant increase in the number of livebirths in non-tertiary hospitals from 1999 onwards. Women who gave birth to an outborn infant were more likely to be a teenager, a multigravida, experience spontaneous preterm labour and/or an antepartum haemorrhage and to give birth vaginally compared with mothers of inborn infants. Outborn livebirths <32 weeks’ gestation had double the risk of mortality compared with inborn peers. Outborn livebirths <28 weeks’ gestation had triple the risk of mortality compared with inborn peers. The disparity in mortality rates in outborn compared with inborn 23-27 week infants widened between 2005 and 2009, whereas it had been narrowing in 1990-2004. Infants born between 28 and 31 weeks’ gestation had similar mortality rates as their inborn gestational age peers in 2005-2009. Risk factors independently associated with an increased risk of infant mortality were outborn birth, multiple pregnancy, an antepartum haemorrhage, vaginal birth, male sex, and diminishing gestational age. In Victoria in 2010-2011, 1,009 infants, 23-31 weeks’ gestation were resuscitated at birth and offered neonatal intensive care. No 22-week livebirths survived. The mortality rate in the outborn infants transferred to a tertiary centre and admitted to a NICU was not significantly different to the mortality rate of the inborn 23-27 or 28-31 week infants. For this cohort, risk factors independently associated with mortality were vaginal birth, diminishing gestational age, lower birth weight and an Apgar score <7 at five minutes of age. Outborn birth and male sex were no longer independently associated with an increased risk of mortality. CONCLUSION This study identified maternal risk factors associated with birth in a non-tertiary hospital and infants at increased risk of perinatal and infant mortality. Although many maternal risk factors contributing to birth in a non-tertiary hospital were not preventable, women who require close surveillance during pregnancy were identified. Prompt in-utero transfer of high-risk pregnancies