Abstract 1429

While both immaturity and very low birth weight have been significantly associated with the development of retinopathy of prematurity (ROP), being severely growth retarded, i.e. small for gestational age has not been identified as a risk factor. We reviewed the effect of birth weight at each gestational age in a population of immature infants at risk for ROP.

We evaluated prospectively collected data from all newborn infants cared for by Baylor College of Medicine physicians at the Harris County Hospital District and born from January 1988 through December 1995 with birth weights less than 1500 grams or gestational ages 23-32 weeks and who survived to be discharged home. Severity of ROP was staged utilizing the International Classification of ROP. During the study period, the same two pediatric ophthalmologists performed all of the ROP screening. A z-score for each infant's weight at their gestational age was determined using the data of Usher and McLean (J Pediatr 74:901, 1969). Z-scores for infants meeting criteria for threshold ROP and those who did not were compared using t-tests. A z-score of 1.0 reflects that the infant's weight is one standard deviation above the mean weight for that gestational age whereas a z-score of -1.0 reflects that the infant's weight is one standard deviation below the mean weight for that gestational age.

During the study period, there were 78,796 live births of whom 1579 met the entry criteria. Of these 1579 study infants, 94 (5.9%)developed threshold ROP and underwent operative intervention. The mean z-score for the non-threshold ROP infants was 0.16 compared to a mean z-score of -1.1 for the infants meeting threshold ROP criteria (P < 0.001). Only 25% of all infants meeting threshold ROP criteria have a z-score of > -0.21; only 5% have a z-score of > 0.92. On the other hand, 25% of infants who did not meet threshold ROP criteria have z-score of > 1.2 and 5% have a z-score of greater than 3.2.

We speculate that factors at work in the antenatal period may effect how the precursors of the developing retinal vasculature respond to multiple factors after delivery.