**Abstract**

Features of catch-up growth are not well established in very low birth weight infants (VLBW). The aim of this study is to analyze the catch-up growth in height and some factors associated in a cohort of VLBW (<1500 g) from birth to age 14 years. Retrospective registration of weight and height at birth and ages 0.5, 1, 2, 3, 4, 6, 8, 10, 12 and 14 years in a cohort of 170 VLBW have been recorded Anthropometric variables were compared with those from a control group. Sixtynine (40.6%) were small for gestational age (SGA subgroup) and 101 (59.4%) were appropriate for gestational age (AGA subgroup). Thirty-seven (21.8%) were extremely low birth weight (ELBW), and 32 (18.8%) extremely preterm (EPT). At age 2, 4 and 10 years, 49.4%, 78.9% and 87.1% VLBW, respectively, did reach normal height. Between 4 and 10 years of age, only 8.2% of VLBW reached normal height. At 10 years of age, 7% of VLBW (1000–1500 g) and 35% of ELBW (<1500 g) showed short stature (p = 0.001). Almost the entire sample of VLBW with normal height at age 2, 4 and 10 have reached an adequate catch-up growth in weight in the previous evaluations. ELBW, SGA and EPT were found to be independent predictors for inadequate catch-up growth in height at 2, 4, and 10 years of age. The growth pattern of children born preterm has particular features: they have a lower rate and/or slowness in the catch-up growth in height with respect to that described in full-term small-for-gestational-age infants. Catch-up in weight appears to be a decisive factor for catch-up in height, and, on this basis, we recommend a rigorous nutritional follow-up in these individuals. If these measures do not help improve catch-up in height, they may be eligible for the establishment of rhGH therapy.

**Keywords:** Catch-up growth, Extremely low birth weight, Growth pattern, Intrauterine growth retardation, Preterm infant, Very low birth weight infant

### **1. Introduction**

Full-term infants who present with intrauterine growth restriction constitute a varied group with multifactorial conditions. These infants, along with high rates of perinatal morbidity and mortality, undergo an increased risk of cardiovascular

and/or metabolic disease in adult life [1]. They subsequently experience an accelerated compensating growth, known as catch-up growth, which usually ceases at age 2 [2–4]. As a matter of fact, those children whose catch-up is inadequate have low chance to reach a normal size in adult life; that is one of the approved indications for the treatment with recombinant growth hormone [5–8].

Nevertheless, the features of catch-up growth are not well characterized in very preterm infants (<32 weeks of gestation) or very low birth weight infants (<1.500 g). In accordance with current knowledge, there is evidence that supports the need to experience adequate extrauterine growth in order to acquire optimal development of all their organic capacities. The increased survival rate of very low birth weight infants (<1500 g) at present time, as a consequence of the recent advances in obstetric and perinatal care, entails a higher risk of sensorineural morbidity and/or disability [5, 9, 10]. In any case, the follow-up of these patients, even though there is no actual consensus, suggests that this catch-up could extend to a later stage, and so condition the prognosis of adult size [11–18].

Catch-up is defined as a fast paced growth after a period of growth failure whose aim is to approach to the measurements of normal term-born infants [2–4]. When this event fails to develop during the initial stages of life, neurological deficits like behavioral difficulties and neurocognitive deficits in very preterm infants are likely to be found [19–21]. In addition, correlations between rapid and early growth (especially of weight) in preterm-born infants and the progression to metabolic syndrome in adulthood have been reported [19, 22, 23]. There is still poor understanding on the factors that determine when catch-up growth occurs in very preterm infants or very low birth weight infants, but it is well-known that low birth weight, early gestational age and medical complications have a particularly negative effect on postnatal growth [16]. In addition, the catch-up growth in weight in these children, which presents simultaneously to catch-up growth in length, has been less frequently studied, even though it has been proved that caloric intake has a positive impact on postnatal growth in preterm infants [24–27].

The main aim of the work is to perform a longitudinal descriptive study of anthropometric measurements in a group of very low birth weight (VLBW) infants, aged from birth to 14 years of age, and to analyze the features of catch-up growth in height and some of the factors associated in these children.
