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Article Excerpt
Pre-term birth (birth at less than 37 completed weeks gestation) is the second leading cause of neonatal mortality in the United States and accounts for more than 50% of neonatal deaths (Alexander et al., 2003; Centers for Disease Control and Prevention [CDC], 1999). Very low birth weight (VLBW) infants, those weighing less than 1500 grams, explain 0.8% of all live births in the U.S., and 7.3% is identified as extremely low-birthweight (ELBW), weighing 750 to 1000 grams (Bacak, Baptiste-Roberts, Amon, Ireland, & Leet, 2005; CDC, 1999; Saari, 2003; Voss, Neubauer, Wachtendor, Verhey, & Kattner, 2006). Although 5% to 6% of all live births require intensive care, most of these newborns (75% to 80%) are of low or very low birth weight (Morse et al., 2006), and almost all of the infants who survive (Morse et al., 2006) experience a growth deficit following discharge from the hospital (Cooke & Ebleton, 2000; Lemons et al., 2001; Steward & Pridham, 2002).
ELBW infants have been shown to develop a growth deficit during the first few weeks of life, mainly due to the loss of weight at birth that persists throughout the neonatal intensive care unit (NICU) hospitalization. Evidence suggests that even though the rate of weight gain for these infants is similar to intrauterine rate of gain, infants between 24 and 29 weeks gestation do not reach the median birth weight of the reference fetus by the time of discharge. Most of these infants have a discharge weight less than the 10th percentile on an intrauterine growth chart. This deficit, which begins during hospitalization and continues at discharge from the NICU, must be overcome at home (Dusick, Poindexter, Ehrenkranz, & Lemons, 2003; Ehrenkranz, 2000; Ehrenkranz et al., 2006; Steward & Pridham, 2002).
Although the CDC has clearly defined growth patterns for full-term infants, the patterns are less well defined for the ELBW infant following discharge from the NICU (CDC, 2007). Because research has shown that these infants experience growth deficits once discharged, it is important to fully understand their growth patterns in order to address the treatment needs of this population and to provide accurate information to parents regarding expected growth milestones and catch-up growth.
Growth Patterns
Growth patterns are best described as fluctuations in the growth trajectory evidenced by accelerations and decelerations in daily weight gain. Controversy abounds regarding the potential for pre-term low birth weight (LBW) infants to catch up to the typical growth pattern of the normal birth weight term infants of the same age. Studies support both sides of the controversy (Dusick et al., 2003; Ford, Doyle, Davis, & Callanan, 2000; Gibson, Carney, Cavazzoni, & Wales, 2000; Korhonen, Hyodynnaa, Lenko, & Tammela, 2004; Morley & Lucas, 2000; Saigal, Stoskopf, Streiner, & Burrows, 2001; Sridhar, Bhat, & Srinivasan, 2002). Sridhar et al. (2002) found late or poor catch-up growth patterns in the weight, length, and head circumference of infants with birth weight less than 1.25 kg and less than 30 weeks gestation, while infants with birth weights greater than 1.25 kg reached the same levels as term appropriate for gestational age (AGA) infants by 1 year of age.
Findings from data collected on 106 children born weighing less than 1500 grams suggest these children were significantly shorter and lighter, and had smaller head circumferences than normal controls at 2, 5, 8, and 14 years of age (Ford et al., 2000). Likewise, at 7 years of age, VLBW children, born under 1500 grams, were shorter than their normal counterparts (Korhonen et al., 2004). The growth of AGA and small for gestational age (SGA) VLBW infants at 2 years of age was also shown to predict the growth of these infants at preschool time, with some pre-school children remaining short in height (Trebar, Traunecker, Selbmann, & Ranke, 2007). Each of these studies, however, included VLBW and ELBW infants together in a portion or all of their data analyses. The combining of these two groups of infants makes it difficult to differentiate the growth patterns of the VLBW infant and the ELBW infant.
Researchers have shown that weight for age z-scores for ELBW infants declined substantially up to the age of 3 years, while height for age z-scores were less at 1, 2, 3, and 8 years of age (Saigal et al., 2006). Additionally, researchers found that by 18 to 22 months corrected age, 40% of VLBW and ELBW infants had lengths, head circumferences, and weights less than the 10th percentile (Dusick et al., 2003), and by 2, 5, 8, 14, and 20 years of age, ELBW infants' height z-scores were significantly below in comparison to term infants (Doyle, Faber, Callanan, Ford, & Davis, 2004). When compared to published population norms, ELBW infants born before 25 weeks 6 days gestation were found to be smaller in weight, head circumference, length, body mass index, and mid-upper arm circumference at 30 months (Doyle et al., 2004).
In contrast, researchers studied the growth of two groups of ELBW infants (< 750 grams and 751 to 1000 grams) and found that at one month post-discharge, the rates of weight gain and head circumference growth suggested some growth recovery at follow up (Ernst, Radmacher, Rafail, & Adamkin, 2003). Likewise, findings from data collected on 1338 children born before 32 weeks gestation and weighing less than 1500 grams suggests that children who were AGA at birth reached heights equal to normal counterparts by 10 years of age (Knops et al., 2005). Furthermore, the head circumference of ELBW infants was found to be 2 SD below the mean on the Nelhaus growth curve (Saigal et al., 2001). Although having lower anthropometric measures compared to a reference population, low birthweight infants were shown to have significant catch-up growth (Xiong et al., 2007). The differences in findings by researchers and the...
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