Sri Lankan fetal/ birthweight charts: validation of global reference for fetal weight and birthweight percentiles.

INTRODUCTION Small for gestational age (SGA) is defined as birthweight below the tenth centile at a particular gestational week. Birthweight centiles for different populations are varied. Generic reference for fetal weight and birthweight that could be adapted to local populations was recently described. The purpose of this study was to validate the reference for birthweights adapted to the local population. METHODS This was a prospective validation study done between January 2012 and July 2012 in well dated pregnancies at General Hospital, Ampara. Observed frequencies of birthweights of 5th, 10th, 50th, 90th and 95th percentiles for Hadlock formula, World Health Organization (WHO) global survey data for Sri Lanka and India were calculated. The expected frequencies for each birthweight centile of our study were compared with observed frequencies. RESULTS A total of 411 patients were recruited and 207 delivered at 40 weeks (40+0-40+6). The mean birth-weight (SD) at 40 weeks of gestation was 3140g (432g). Hadlock formula and WHO reference data for India overestimate and underestimate most of the birthweights respectively. WHO generic reference adapted to Sri Lanka fitted well with our data. The mean birthweight of our population is similar, and the adapted reference range would identify most of the small fetuses correctly. It would also identify almost all the babies with weight above the 90th centile. CCONCLUSIONS The findings of the study show that the observed distribution of birthweight fitted well with the reference range derived from the WHO global reference range adapted to Sri Lankan population. WHO reference charts can be used effectively in Sri Lankan population.