Original articleBody mass index and weight-for-length ratio references for infants born at 33–42 weeks gestation: A new tool for anthropometric assessment
Introduction
Overweight and obesity are recognized as major links in the development of type 2 diabetes mellitus and metabolic syndrome, including an increased risk of cardiovascular disease. In recent years, the prevalence of childhood obesity and obesity-related complications has increased to near-epidemic proportions.1, 2, 3, 4 Observational evidence in human studies suggests that increased maternal weight gain during pregnancy as well as higher birth weight and faster growth in the first months and years of life are associated with overweight in childhood and adulthood.5, 6, 7, 8, 9, 10, 11
Body mass index (BMI), defined as weight in kilograms divided by height in meters squared, is highly correlated with subcutaneous and total body fat.10, 12 BMI is currently the measure used most often to screen for obesity. As suggested by Must et al.13 in 1991 and consensually validated by many authors and organizations, including the US Centers for Disease Control And Prevention, and the European Childhood Obesity Group,12, 14, 15 the 85th and 95th BMI percentiles serve as the cut-offs for defining overweight and obesity in children. Several screening standards have been proposed for the younger pediatric population.16, 17, 18, 19, 20 The American Academy of Pediatrics currently recommends screening for weight-for-length (Wt/L) in all infants from birth to age 2 years, and for BMI in all children starting from age 2 years.21 However, recent studies noted that BMI at birth and weight and BMI gain at age 0–3 and 3–12 months are the best predictors of overweight at age 5–7 years and early adulthood,5, 6, 7, 8, 9, 10, 11 suggesting that BMI screening should start even earlier.
At the other end of the spectrum, malnutrition, defined as a BMI below the 5th percentile, is associated with poor neurodevelopmental outcome. Although relating outcome to BMI or Wt/L ratio percentiles seems appropriate, data in preterm infants are lacking, and most reports focused only on low birth weight. The inclusion of measures of body proportionality, such as BMI or Wt/L, as a routine complementary means to monitor growth in premature infants22 can best be accomplished in areas where gestational-age-specific percentile curves are available. The community-based World Health Organization (WHO) Multicenter Growth Reference Study (MGRS), performed between 1997 and 2003, sought to develop new international growth references for infants and young children,20 but their data did not include premature infants. The design of this project combined a longitudinal study from birth to 24 months of single term birth infants with a cross-sectional study of children aged 18–71 months. A total of 1743 infants from 6 participating countries were enrolled in the longitudinal cohort, 6 of whom were excluded for morbidities affecting growth, leaving a sample of 1737 infants (894 boys, 843 girls). Eligibility criteria for inclusion were: gestational age between 37–42 completed weeks, single birth, absence of significant morbidity. Full-term low birth weight infants (<2500 g, 2.1%) were not excluded.
In 2008, our group published growth charts based on the birth weight, birth length, and head circumference of infants born at 24–42 weeks gestation at a major tertiary medical center in Israel.23 The overall objective of the present study was to use these data to compute, for the first time, BMI and Wt/L growth references for the Israeli population of infants born at 33–42 weeks gestation. The specific objective was to determine the external validity (generalizability) of our charts by comparing our data for full-term infants (37–42 weeks gestation) with the WHO growth-curve data.
Section snippets
Methods
The Beilinson Computerized Medical Birth Registry was searched for all live-born singleton neonates delivered at 24–43 weeks gestation from 1991 through 2005. Data on birth weight and birth crown-heel length were collected. At our center, birth weight is routinely measured in the naked infant within 1 h of delivery by highly trained nurses using electronic scales that are accurate to 5 g and are calibrated before each measurement. Crown-heel length is measured at the same time to the nearest
Results
In the current study, birth weight and birth length measurements at 37–42 weeks were available for 77599 and 62794 infants, respectively (combined sex). Of the full-term infants, 3.25% weighed <2500 g at birth. BMI and Wt/L ratio were calculated for 30851 female and 32327 male infants born at 33–42 weeks.
Table 1, Table 2 summarize the percentiles of birth weight, birth length, and BMI in female (Table 1) and male (Table 2) neonates born at Rabin Medical Center at 37–42 weeks gestation and the
Discussion
The growth reference percentiles for BMI and Wt/L ratio presented by us derived from a large representative sample of singleton neonates born in our center at 33–42 weeks gestation. Our results can be considered valid in terms of the 2 main challenges in formulating reference growth curves for newborns: gestational age assessment,26 and implausible birth weight for gestation.27 The increased reliance on early fetal ultrasound-based estimates of gestational age in our center decreased the rate
Conflict of interest
There are no conflicts of interest.
Author agreement
All authors have made substantial contributions and final approval of the conceptions, drafting, and final version.
Author responsibility
The authors’ responsibilities were as follows:
SD supervised the study during its entire duration, analyzed some of the data (percentile measurements) and wrote the initial draft of the manuscript; RS contributed substantially to the preparation of the manuscript; SD and RS drafted the manuscript, contributed to the revision and approved the final version of the paper; DF was involved in the initial design of the study, conducted the literature review and helped with the initial draft of the
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