Defining the Expected Growth of the Preterm Infant



The infant mortality rate, defined as the number of children who die before 1 year of age per 1000 live births, has long been considered a measure of a population’s health. The subspecialty of pediatrics now known as neonatology and the Neonatal Intensive Care Unit (NICU) arose from efforts to decrease infant mortality. Access to neonatal intensive care has improved the survival rate of those infants with birth trauma, asphyxia, bacterial infections, and congenital anomalies. Additionally, the miniaturization of technology has made it possible to challenge the lower limits of viability by providing cardiopulmonary support to smaller and prematurely born infants. However, the incidence of low birth weight has not decreased and the incidence of preterm birth is continuing to increase. Providing the care to support the development of the extremely premature infant in an extrauterine environment is an ongoing challenge for all perinatal care providers. Pediatricians agree that nutrition and growth of prematurely born infants in the NICU should be similar to growth in utero. However, in utero nutrition requirements and growth are poorly defined. Multiple investigators have reported values for anthropometric measurements for premature infants, but the values are not coincident. This chapter compares the differences in recently defined growth patterns of preterm infants from 22 to 37 weeks gestation and describes differences in early growth patterns according to race and gender. Additional data are presented to describe the necessary caloric intake to support reasonable growth.


Birth Weight Preterm Infant Neonatal Intensive Care Unit Head Circumference Growth Velocity 
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Constant for Equation (37.1)


Appropriate for gestational age


Constant for Equation (37.1), growth velocity for weight


Birth weight (g)


Constant for Equation (37.2), growth velocity for head circumference


Constant for Equation (37.3), growth velocity for length


Variable in Equations (37.4) and (37.5)


Variable in Equations (37.4) and (37.5)


Black female


White female


Gestational age (weeks)


Growth velocity in Equation (37.4)


Head circumference (cm)


Length (cm)


Large for gestational age


Last menstrual period


Black male


White male


Neonatal intensive care unit


10th percentile in Equation (37.7)


50th percentile in Equation (37.7)


90th percentile in Equation (37.7)


Small for gestational age


Variable in Equations (37.4) and (37.5)


Variable in Equations (37.4) and (37.5)


Z-score in Equations (37.6) and (37.7)




Standard deviation



The authors would like to acknowledge and thank Dr. Mildred T. Stahlman, MD for her ongoing support and encouragement to pursue this work.


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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  1. 1.Department of Radiology and Radiological SciencesVanderbilt UniversityNashvilleUSA
  2. 2.Pediatric Nurse PractitionerNashvilleUSA

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