Outcomes of children of extremely low birthweight and gestational age in the 1990's
Introduction
The improved survival of extremely immature and low birthweight infants in the early to mid 1990's resulted mainly from an increase in the use of assisted ventilation in the delivery room and surfactant therapy 1, 2. The reports of neonatal morbidity and early childhood outcomes for this period have only recently appeared in the literature; many, as yet in abstract form. The majority of reports from the United Kingdom 3, 4, 5, 6, 7and Australia 8, 9, 10are regional. In contrast, reports from Japan [11], Canada 12, 13, 14, 15, 16, 17, 18, 19and the United States 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33represent mainly individual centers or multicenter networks. Europe has few reports 34, 35.
This review will examine the survival, neonatal morbidity and early childhood neurodevelopmental outcomes of infants born at the limits of viability during the 1990's, or prior to this time if surfactant therapy was used, and discuss the factors which influence outcomes. These include maternal demographic descriptors, complications of pregnancy and reasons for the early delivery, maternal and fetal therapies, gestational age assessment, obstetrical attitudes including the use of caesarean sections, and delivery room and neonatal practices and therapies. Methodological considerations when measuring mortality and early childhood outcomes include whether to examine outcomes by gestational age or birthweight, population selection, the categorization of the various neonatal morbidities and later neurodevelopmental outcomes, and the time periods considered
Prior to the 1990's outcomes were mainly considered by birthweight rather than by gestational age [36]. This was related to the uncertainty of the obstetrical gestational age in many instances, when early ultrasound confirmation of gestational age was less common, and to the poor reliability of the postnatal assessment of gestational age. Availability of information on the short and long term outcomes according to gestational age rather than birthweight became more important as survival improved and decisions needed to be made as to the timing and mode of delivery, in the face of extreme immaturity or maternal complications. This information is also critical when deciding whether to actively resuscitate an extremely immature infant. Since there is serious concern and debate about the treatment of extremely small infants in general, this review will consider reports of survival, neonatal morbidity and early neurodevelopmental outcomes by both birthweight (less than 800 g) and gestational age (less than 26 weeks) 37, 38, 39.
Section snippets
Survival by gestational age and birthweight (Table 1 and Table 2)
Definitions of viability have differed and include the ability to sustain independent life 40, 41, to sustain life with the aid of a ventilator [42], to survive following intensive care [5], or to live and to grow and develop normally [43]. In many parts of the world, infants born as early as 23 weeks gestation are considered viable and actively treated since they have the potential for later sustaining independent life and in some cases, developing normally. This has been termed “marginal
Neonatal morbidity (Table 3 and Table 4)
The major morbidities which have an influence on later development include chronic lung disease, severe brain injury, necrotizing enterocolitis, nosocomial infections and retinopathy of prematurity 27, 31, 71, 72, 73, 74. Additional neonatal factors associated with later outcomes include transient hypothyroxinemia and breastmilk feeding 75, 76. Morbidity increases with decreasing gestational age and birthweight (Table 3, Table 4), and varies according to demographic and clinical therapeutic
Early childhood neurodevelopmental outcomes (Table 5 and Table 6)
The majority of reports of early childhood outcomes consider children as being severely disabled or impaired if they have either a major neurologic abnormality such as cerebral palsy, unilateral or bilateral blindness, deafness requiring hearing aids and/or cognitive functioning less than two standard deviations of the mean (Mental development <68 or <70) [83]. These measures have been criticized, however few measures of functioning and quality of life have been validated during early childhood
The <500 g birthweight infant
The World Health Organization has suggested excluding <500 g birthweight infants from analyses of perinatal outcomes, but <500 g birthweight stillbirth and livebirth infants are included in the perinatal mortality statistics of the United Kingdom, USA and Canada 6, 59, 90. The small proportion of <500 g birthweight infants who survive following active delivery room resuscitation usually represent a select group of predominately female, small for gestational age infants. There have previously
Childhood morbidity and growth
There have been few reports specifically pertaining to childhood illnesses and growth of extremely low gestational age and birthweight children. Many infants are discharged home on oxygen and apnea monitors, and require rehospitalizations for respiratory complications associated with the chronic lung disease. Sixty percent of 500 to 699 g birthweight survivors treated with surfactant between 1987 and 1989 required rehospitalization, and 10% were oxygen dependent due to their chronic lung
Effects of surfactant and steroid therapy
Surfactant and antenatal steroid therapy are considered to be the major determinants of the improved survival of very low birthweight infants in the 1990's 2, 55, 99, 100. Many mothers at high risk for preterm birth currently receive weekly antenatal steroid therapy from 24 weeks gestation and the majority of infants born at less than 28 weeks gestation also receive postnatal steroids to prevent or treat chronic lung disease. Antenatal steroids are considered to stabilize postnatal blood
Conclusion
Survival of extremely low birthweight and gestational age infants increased in the early 1990's due to the combined effects of an increase in assisted ventilation at delivery, surfactant therapy and possibly increased use of antenatal steroid therapy. The gestational age of viability, which is considered to be 23 to 24 weeks gestation has not changed, but survival increased at these limits of viability. Although further increases in survival during the mid 1990's have been reported these appear
Acknowledgements
We would like to thank Mrs. Eloise Scott and Mrs. Harriet Friedman for their participation in our follow-up program, and Mrs. Joyce Nolan for assistance in the preparation of the manuscript.
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