Preterm Infants: Risk for Death Estimated More Precisely

Jennifer Garcia

February 07, 2012

February 7, 2012 — Rather than using gestational age (GA) alone, a new study published online February 6 in the Archives of Pediatric and Adolescent Medicine also used male sex, sex-specific birth-weight percentile, and lack of prenatal steroid therapy to more accurately estimate the combined outcomes of deaths or severe morbidities of infants born at 24 to 26 weeks' gestation.

The national, population-based study estimated outcomes as the sum of the percentages determined for 4 parameters — gestational age (26, 25, and 24 weeks), birth-weight percentile (>75th, 25th - 75th, and <25th percentiles), lack of prenatal steroids, and male sex — and incorporated them into a linear regression model. The researchers collected data from the Israel National Very Low Birth Weight Infant Database for infants born at 23 to 26 weeks' gestation between 2000 and 2008, and included information on 2544 infants.

The model demonstrated a "cumulative risk of 17% for each GA week less than 26 weeks, 13% for each birth weight percentile group below the 75th percentile (25th to 75th and <25th percentiles), 16% for no exposure to prenatal corticosteroid therapy, and 7% for male sex," write Amir Kugelman, MD, from the Department of Neonatology, Bnai Zion Medical Center, Technion–Israel Institute of Technology, Haifa, and colleagues.

The authors continue: "The intercept value was 25%. The intraclass correlation coefficient between the observed and estimated poor outcomes was 0.93 (95% [confidence interval], 0.82 - 0.94), indicating a high level of agreement between observed and estimated rates."

To illustrate the utility of the model, the researchers calculate the risk of a male infant born at 25 weeks' gestation with a birth weight of 800 g at 62%: "17% for 25 weeks' [gestational age], 13% for birth weight in the 25th to 75th percentile group, 0% for prenatal steroid therapy, 7% for male sex, and 25% intercept." The observed rate of poor outcomes in this group was 66% (99/151 infants).

In all 3 GA week groups, lack of prenatal steroids demonstrated odds ratios (ORs) of from 2.00 to 2.56, whereas in the 25 and 26 weeks' gestation groups, male sex was significant (ORs, 1.52 and 1.41, respectively).

"Our ability to predict long-term outcomes is limited at birth, during the first days and weeks after birth, and during prolonged hospitalizations. Extremely low-birth-weight infants are at ongoing risk for medical morbidities and other adverse events that may influence their prognosis.... Thus, assessment of the risks of major morbidities occurring during the neonatal period and the risk of mortality are of concern to parents and caregivers," the authors note.

The researchers defined poor neonatal outcomes as death or severe neurologic or pulmonary morbidities at discharge. These morbidities have been associated with poor long-term neurodevelopmental outcomes. Any of the following was considered severe neurologic morbidity: grade 4 periventricularintraventricular hemorrhage, posthemorrhagic hydrocephalus, periventricular leukomalacia, or grade 4 retinopathy of prematurity. Oxygen supplementation at 40 weeks' postmenstrual age or home oxygen therapy was used to define severe pulmonary morbidity.

The authors acknowledge that the study has limitations, which include its observational design and variations in obstetric attitudes that may influence clinical practice. In addition, long-term neurodevelopmental assessment would be required to determine whether infants with severe morbidities at discharge will have significant developmental handicaps.

The use of GA alone in estimating infant morbidity has been challenged because of its subjective nature, according to the researchers. The addition of other parameters, also available at the time of birth, may better predict outcomes and aid the physician in determining whether a premature infant requires more intensive care.

"The percentage of infants with poor outcomes at discharge decreased significantly with each GA week. However, within each of these GA groups, the estimated rates for poor outcomes varied considerably, depending on the presence of these additional parameters," note Dr. Kugelman and colleagues.

"These results strongly suggest that GA alone should not be used to estimate the likelihood of survival without major neonatal morbidity among extremely preterm infants." The researchers further add that, "These results may help in creating poor outcome estimation tools for other populations that will adopt the principles of our model using their own mortality and morbidity data."

The Israel National Very Low Birth Weight Infant Database is supported in part by the Israel Center for Disease Control and the Ministry of Health. The authors have disclosed no relevant financial relationships.

Arch Pediatr Adolesc Med. Published online February 6, 2012. Abstract

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