Improved method for revising the Israel birthweight references.

Objectives: Birthweight is often used as an indicator of fetal health. Categorization of infants as small or large for gestational age has clinical significance. Due to growth differences between countries, it is important to have local reference data. The aim of the study was to describe an Israel population-based reference of birthweight by gestational age stratified for singletons/multiple births and gender.

Methods: Data on birthweight and gestational age were obtained for the years 2010-2019 from the Ministry of Health Birth Registry. Implausible birthweight and gestational age values were excluded in a two step process. First, overtly implausible values were excluded using visual mapping. Then, infants whose birthweight was below or above the fifth interquartile range for each completed week were excluded.

Results: During the 10-year period there were 1,761,884 infants delivered in Israel; 1,689,696 were included in the analysis. 4.4% of the live born infants were from multiple births. The mean birthweight of singletons (3251 g) was 947 ± 4 g higher than that of multiples (2304 g). The birthweight of the male multiple births began to differ from that of the singletons at 30 weeks; female multiple births began to deviate at 31 weeks. The increase in birthweight of singletons leveled after 42 weeks and those born after 43 weeks weighed less than infants born earlier. Comparison of the curves for singletons from the present study to those reported for the years 1993-2001 reveal a similar median but significant differences in the distribution of lower and higher percentiles.

Conclusions: Improved data collection and validation permitted inclusion of 96% of births for analysis. Use of interquartile range distribution to exclude values of birthweight/gestational age that were implausible improved validity. Compared to curves reported previously, changes were found in the distribution of birthweights for the upper and lower percentiles. Periodic updates of growth curve references are important.