Female sex, exposure to prenatal corticosteroid therapy, singleton birth, and increased birth weight (in 100-g increments) each improve an infant's chances of a positive outcome with intensive care.
The magnitude of the benefit is similar to that of an extra week of gestational age, Dr. Jon E. Tyson and his associates at the National Institute of Child Health and Human Development (NICHD) wrote in the April 17 New England Journal of Medicine.
Decisions about admitting extremely premature infants to intensive care are “highly controversial,” with most centers in the United States selecting patients solely on the basis of gestational age thresholds. “Such care is likely to be routinely administered at 25 weeks' gestation but may be provided only with parental agreement at 23–24 weeks, and only 'comfort care' may be given at 22 weeks,” the investigators noted.
The researchers assessed a cohort of 4,446 infants born at 22–25 weeks' gestation at 19 medical centers in the NICHD's neonatal research network between 1998 and 2004. At a corrected age of 18–22 months, 49% of the study subjects had died, and 61% had died or sustained profound impairment.
Factors that might contribute to outcome were examined, and the four listed above were found to significantly improve the rates of survival and survival without impairment. The improvements were equivalent to a 1-week increase in gestational age, said Dr. Tyson of the University of Texas at Houston and associates.
“For example, among infants born midway between 24 and 25 completed weeks of gestation, the estimated likelihood of death or profound impairment was 33% for a 750-g, appropriate-for-gestational-age female singleton who received prenatal corticosteroids, but 87% for a 525-g, small-for-gestational-age male twin who did not receive prenatal corticosteroids,” they wrote.
Even among the highest-risk infants—those born before 24 weeks with a birth weight of 600 g or less—outcomes varied considerably according to these four risk factors. The maximum potential rate of survival without profound impairment was as low as 5% for boys weighing 401–500 g born at 22 weeks, but as high as 38% for girls weighing 501–600 g born at 24 weeks (N.Engl. J. Med;358:1672–81).
Nevertheless, in actual practice it turned out that girls were less likely than boys and that singletons were less likely than multiples to receive intensive care when they had the same likelihood of a favorable outcome.
Weighing the additional four factors into the decision “is likely to promote treatment decisions that are less arbitrary, more individualized, more transparent, and better justified than decisions based solely on gestational-age thresholds,” the investigators said.
To assist physicians faced with such decisions, the authors provided a Web-based tool (www.nichd.nih.gov/neonatalestimates
Dr. Tyson and associates added that in assessing outcomes, they included factors such as treatment cost, resource use, parental distress, and “infant suffering due to painful procedures, prolonged intubation, and such complications as intracranial hemorrhage, necrotizing enterocolitis, and recurrent episodes of hypoxia.”
“Barring major therapeutic advances, our findings indicate that extending intensive care to all of the most immature infants would entail considerable suffering, resource use, and cost in order to benefit only a small proportion of infants,” they noted.