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Table 1 Details of the Data Sources

From: A new growth chart for preterm babies: Babson and Benda's chart updated with recent data and a new format

  Kramer [8] Niklasson [11] Beeby [12] CDC [13]
Data used Birthweight ≤ 40 weeks Head and length measures ≤ 40 weeks Head and length measures ≤ 40 weeks Weight, head and length measures after term
Sample size (n) 676,605 376,000 Head circumference: 29090 and length: 26973 Birth data :weight: 82 million, length: 900,000, head circumference: 400. First year of life: 2200 to 38,000 infants.
n < 30 weeks 4101 0 274 N/A
Gestational age range of study 22 to 43 weeks 28.5 to 42.5 weeks 22 to 43 weeks Post term
Inclusion criteria All births "Healthy" newborn infants Singleton livebirths NHANES surveys
Exclusion criteria Ontario (province) was excluded due to problems with data quality. Stillbirths, twins, complications during pregnancy with potential effects on fetal growth and significant malformations Multiple births Infants with birthweights < 1500 grams
Dates 1994 to 1996 1977 to 81 1982 to 1995 Primarily 1963 to 1994
Completed gestational weeks yes yes yes N/A
Method to assess gestational age "early ultrasound has increasingly been the basis for gestational age assessments in recent years" Last menstrual period was used when it was in agreement (+/- 2 weeks) with the obstetric assessment. If not, the latter was used. When either estimate was missing the gestational age was considered unknown. In the majority of cases the gestational age was based on first trimester ultrasound, or when early ultrasound was not available, last menstrual period dates were used. In < 1% of cases, the Ballard assessment was used when neither dates nor ultrasound were available. N/A
Outliers Assumed a log normal distribution of birthweight at each gestational age and compared the probabilities of accurate versus misclassification of infant's gestational age.   The mother's medical record was examined and following verification of the gestational age and other data, outliers were either accepted as real or corrected. Curves were smoothed with a variety of parametric and non-parametric procedures