New and improved Israeli reference of birth weight, birth length, and head circumference by gestational age: a hospital-based study.

BACKGROUND Many centers in Israel still use pre-1970 reference data for neonatal weight, length and head circumference. A recently published population-based reference overestimated the weight of premature infants. OBJECTIVE To develop a national reference for birth weight, birth length and head circumference by gestational age for singleton infants in Israel. METHODS Data were collected on all singleton live births documented in the neonatal registry of Rabin Medical Center from 1991 to 2005 (n=82,066). Gestational age estimation was based on the last menstrual period until 1977 and early fetal ultrasound thereafter. Neonates with an implausible birth weight for gestational age (identified by the rule of median +/- 5 standard deviations or expert clinical opinion) were excluded. Reference tables for fetal growth by gestational age were created for males and females separately. RESULTS The growth references developed differed markedly from the Usher curves currently used in our department. Compared to the recently published population-based birth weight reference, our data were free of the problem of differential misclassification of birth weight for gestational age for the premature infants and very similar for the other gestational age groups. This finding reinforced the validity of our measurements of birth weight, as well as of birth length and head circumference. CONCLUSIONS Use of our new (birth length and head circumference) and improved (birth weight) gender-specific hospital-based reference for fetal growth may help to define normal and abnormal growth in the neonatal population of Israel and thereby improve neonatal care and public health comparisons.