[Birth weight and size: charts and equations].

OBJECTIVES: To construct new reference charts and equations for birth weight and birth size using a large and exhaustive sample of newborns. To compare this new references with previous ones. MATERIALS AND METHODS: The study data were obtained from a single health authority (the birth registry of Yvelines, a French Territorial division of 1.4 million people) over 3 years. Multiple pregnancies were excluded. No data were excluded on the basis of abnormal biometry or birth weight. For each measurement, a least square regression model with high order polynomials was fitted to predict mean, standard deviation and therefore Z scores of birth weigh and birth size at any gestational age at birth from 25 to 42 weeks'. RESULTS: There were 58934 and 56956 measurements included for weight and size at birth respectively. New charts and equations for Z scores calculations, adjusted for sex, are reported based on polynomial regression methods. CONCLUSION: We present new French reference charts and equations for birth biometrics. Because they were derived from a very large and unselected sample, there might be more relevant to clinical practice than others and can be easily used to compute centiles and Z-scores.