Growth curves: how to best measure growth of the preterm infant.

Birth weight is one of the most important anthropometric measures in the evaluation of an infant. For the full-term infant, birth weight is compared with reference or standard growth curves that are constructed by plotting weight, length, and head circumference against postnatal age. Following a similar approach for preterm infants is less effective for a variety of reasons. Birth weight and other anthropometric measures used to evaluate an infant at birth are influenced by various maternal characteristics, the intrauterine milieu, and duration of gestation. Second, the causes of premature birth and their impact on birth weight are largely unknown. Third, gestational age is difficult to determine with full certainty. One approach that has been used to circumvent these issues is to use intrauterine growth reference curves. However, these curves do not really reflect "normal" growth because they were constructed using cross-sectional data from infants born prematurely and, as such, do not reflect the normal condition. Thus, there is a need to develop normative growth curves derived from "healthy" preterm infants that can be applied to neonates born prematurely. These should be updated periodically to reflect secular trends in maternal body weight, height, and overall health.