Table 1

Details of the data sources
Voight, 2010 Olsen, 2010 Kramer, 2001 Roberts, 1999 Bonellie, 2008 Bertino, 2010 WHO, 2006
Data source German Perinatal Survey Pediatrix Medical Group hospitals Canadian national file Australian National Perinatal Statistics Unit Scottish maternity data collection Italian Neonatal Study WHO multicentre growth reference study
Sample size 2,300,000 130,111 676,605 734,145 100,133 45,462 882
n < 30 weeks 14146 11377 3247 3193 2053 623 N/A
Lowest gestational age 22 23 22 20 24 23 term
Dates 1995 to 2000 1998 to 2006 1994 to 1996 1991 to 1994 1998 to 2003 2005 to 2007 1997-2003
Data Weight Weight, head, length Weight Weight Weight Weight, head, length Weight, head, length
Exclusion criteria None stated, included both live and stillborn Multiple births, congenital anomalies, death before discharge, outlier measures (> 2 x interquartile range below the first and 3rd quartile). Ontario province was excluded due to problems with data quality. Omitted multiple and still births (births < 400 grams did not need to be recorded) Multiple births, lethal anomalies, weights < 250 grams, and outlier measures (> 2 x interquartile range outside the first and 3rd quartile). Multiple births, stillbirths, major congenital anomalies, and fetal hydrops Maternal smoking, not breastfeeding, solids before 4 months. Screened for environmental or economic constraints.
Method to assess gestational age Ultrasound assessment 8–14 weeks and Naegle’s rule. Neonatologist assessment “early ultrasound has increasingly been the basis for gestational age assessments in recent years” Dates, prenatal, or postnatal assessment Clinician assessment based on ultrasound, maternal dates, and clinical estimates Ultrasound assessment first trimester Not stated
Outliers/smoothing method Cubic regression, LOESS smoothing, LMS parameter smoothing LMS methods, with the skew set to one and further manual smoothing Assumed a log normal distribution of birthweight at each gestational age and compared the probabilities of accurate versus misclassification of infant’s gestational age Omitted outlier measures (> 2 x interquartile range below the first and 3rd quartile). Cubic spline fitting Generalized logistic functions Omitted outliers > 3 SD, LMS parameter smoothing, skew set to one for weight, cubic spline fitting.

Fenton and Kim

Fenton and Kim BMC Pediatrics 2013 13:59   doi:10.1186/1471-2431-13-59

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