Postnatal Development of Urea Synthesis Capacity in Preterm Infants with Intrauterine Growth Retardation

Abstract

The postnatal development of the urea-synthesizing capacity was studied in 21 preterm infants with intrauterine growth retardation (IUGR) and compared with results found in 12 infants without IUGR as controls. The urea-synthesizing capacity was estimated by the ratio Q of ¹⁵N abundance of ammonia and urea in 6-hour urine samples collected after enteral administration of 3 mg [¹⁵N]H₄Cl/kg body weight. The measurements were performed on the first day when a protein intake of 3.0–3.5 g/kg/day and an energy intake of 120 kcal/kg/day were tolerated (study day 1: postnatal 14–21 days) and on the day of discharge from the hospital (study day 2: postnatal age 39–56 days). The group of infants with IUGR was subdivided in one group of infants who developed catch-up growth (n = 12) and one group who did not demonstrate catch-up growth (n = 9). On study day 1, the Q values of the IUGR infants without catch-up growth were significantly higher than those of the IUGR infants with catch-up growth (13.4 ± 2.3 vs. 9.2 ± 2.2) or of the control infants without IUGR. During the time period from study day 1 to study day 2 the Q values of the IUGR infants with catch-up growth decreased significantly (9.2 ± 2.2 vs. 4.8 ± 2.0; p < 0.001) and were in the range of the control infants without IUGR. In contrast, the Q values of the IUGR infants without catch-up growth did not significantly change during the study period (13.4 ± 2.3 vs. 11.3 ± 2.8; p = 0.097). On both study days there was a significant correlation between the Q values and the degree of IUGR (study day 1: r = 0.652, p < 0.01; study day 2: r = 0.842, p < 0.001). The data indicate that the urea-synthesizing capacity of preterm infants increases during early postnatal life and that severe IUGR may impair this development. Metabolic investigations using urea as marker for evaluation of optimal quantity or quality of dietary proteins should carefully be interpreted when infants with severe IUGR are studied.

Impact of placental insufficiency on fetal skeletal muscle growth

“…Preterm SGA infants have higher metabolic rates and increased energy expenditure when compared to AGA infants in the first month of life (Bohler et al, 1999, Chessex et al, 1984, Davies et al, 1996). Some studies show that SGA infants are more efficient at protein gain (Cauderay et al, 1988, Van Goudoever et al, 1995), and others indicate that SGA infants have deficiencies in protein metabolism (Boehm et al, 1988, Boehm et al, 1998). We do not have a clear understanding of how to best provide nutrition to the IUGR neonate, especially when they are born preterm and require supplemental nutrition either by enteral or parenteral nutrition.…”

Adjustable fortification of human milk fed to preterm infants

“…Thus, early studies suggested BUN is not a valid measure of protein intake in preterm infants. 4,[9][10][11] More recent studies, one by this group, 12 suggest otherwise in the clinically stable preterm infant. 13 In the latter study, the relationship between nitrogen accretion and growth fed two levels of protein intake, 3.0 and 3.6 g/100 kcal, was assessed.…”

Birth weight – a risk factor for progression in diabetic nephropathy?

“…Recently, a direct relation between birth weight and number of glomeruli in humans has been suggested in a morphological study [7], however, birth weight/length ratio may be a more sensitive measure of IUGR [8]. Other groups have also found evidence of impaired renal function in newborn suffering from IUGR [3, 4]. Brenner and Chertow [9] originally suggested that reduced glomerular filtration capacity, as seen in individuals born with fewer functioning nephrons, predicts susceptibility to systemic and glomerular hypertension and kidney disease later in life [13].…”

“…[1]. Intrauterine growth retardation (IUGR) may lead to congenital retardation of renal development [2–4] and a reduction in nephron number [2, 5, 6]. One clinical expression of IUGR is low weight at birth, and this has recently been associated with reduced number of glomeruli in humans [7].…”