Birthweight standards for south Indian babies.

OBJECTIVE To obtain birthweight standards for south Indian babies. DESIGN Prospective cohort study. SETTING A tertiary care hospital in south India. PATIENTS AND METHODS Data from 11, 641 singleton live births between 1991 and 1994 were used to calculate smoothed gestation specific birthweight centiles for four categories based on sex of the infant and birth order. Smoothed gestation specific birthweight centiles were also calculated for all births between 37-41 weeks without adjustments for sex of infant or birth order. Data for births between 37 and 41 weeks were reanalysed using non-adjusted birthweight centiles and birthweight centiles adjusted for sex and birth order to determine misclassification of data. Multiple regression analysis was used to determine the influence of various variables on birthweight. RESULTS Factors influencing birthweight were gestation at birth, sex of infant, birth order and maternal height. A quadratic equation including these variables and the square of the gestational age explained 18% of variation in birthweight. Female infants were on the average 113 g (95% CI 26-200 g) lighter than male infants. Later born babies were on the average 130 g (95% CI 40-220 g) heavier than first born babies. Therefore significant misclassification of infants occurred when non-adjusted birthweight centiles were used. Babies born to women whose heights were outside the interquartile range (150-158 cm) were 81 g lighter or heavier than those born to women within this range. CONCLUSIONS Birthweight centiles for gestation when used should be adjusted for birth order, sex of infant and maternal height.