Patterns of postnatal weight changes in infants with very low and extremely low birth weights

To describe (1) short-term postnatal weight loss and gain patterns in infants with very low and extremely low birth weights and (2) the variables that may affect these weight change patterns.

Descriptive, retrospective review.

University hospital in the intermountain western United States.

Sixty-two charts of infants admitted to a university neonatal intensive care unit from July 1990 through November 1992 were reviewed. Infants who weighed 1000 grams or less were categorized as extremely low birth weight (ELBW) and infants weighing 1001 to 1500 grams were categorized as very low birth weight (VLBW). Each group was comprised of 31 infants. Fifty percent of the sample were male, and 50% were female. Eighty-five percent of the sample were Anglo-American, and 15% were non-Anglo-American.

Data were collected on a three-part data collection tool and included demographic and treatment variables.

A significant difference was found in the maximum percent weight lost between the two groups, with the ELBW group losing a mean of 14.77% of birth weight and the VLBW group losing a mean of 11.35% of birth weight (t = 2.45, p < 0.05). The day the infants reached their nadir weight was significantly different between the two groups. The ELBW group reached their nadir on day of life 7, and the VLBW group reached their nadir on day of life 6 (t = 2.00, p < 0.05). No significant difference was noted in the time to return to birth weight between the two groups, with a mean of 15 days to return to birth weight. Factors associated with postnatal weight changes were intraventricular hemorrhage, use of diuretics and steroids, day of life when nadir weight occurred, and maximum percent of weight lost. Many of the independent variables were significantly interrelated to each other (r = -0.90 to r = 0.91, p < 0.01 to p < 0.001). However, only the variables that correlated with time to return to birth weight were entered into the regression analysis. These variables included number of days diuretics were given before return to birth weight, maximum percent of weight lost, and day of life the infants reached their nadir weight. Number of days diuretics were given before return to birth weight correlated significantly with time to return to birth weight (r = 0.77, F = 26.66, p < 0.0001) although maximum percent of weight lost and day of life the infants reached their nadir weight had a minimal effect.

Further research into the effects of diuretic therapy on weight changes in this population of infants may lead to interventions to minimize the negative effects of diuretics on return to birth weight. In addition, the older growth charts may not be applicable to this population of infants. Generation of new growth charts that provide growth curves based on these data could be useful in developing nutritional therapies that would promote growth and possibly decrease the length of hospital stay for these infants.