A need for an update of Polish birth weight reference norms

Abstract

The indicators of perinatal outcome are birth weight and gestational age. The standard method of assessing the outcome is comparing the newborn’s birth weight with the reference system, presented in the form of percentile charts. Acceleration or delay in prenatal development, which are associated with environmental changes, stress the need to validate the developmental norms. The goal of this study is to evaluate the need to construct new and accurate reference standards. The study includes data of newborns from singleton pregnancies: 4919 born in 2000 and 3683 born in 2015. Study variables included gestational age, sex, and birth weight. Percentile values estimated for two groups of infants born in years separated by a 15-year period, born in 2000 and in 2015, were compared. Birth weight percentiles, from the 28th to the 42nd week of gestation, were calculated using the Lambda Mu Sigma method. Estimated values revealed the birth weight standards in different weeks of gestational age for both years: 2000 and 2015. Comparison among medians estimated for infants born in these years showed the existence of significant differences among boys in the 28th, 36th, and 39th weeks and among girls in the 34th and 41st weeks of gestational age. As the period between the two measurements involves several years, environmental changes during this time period might have significantly affected the course of pregnancy and thus the birth weight. Hence, there is a need to validate the developmental norms. The reference standards should be renewed, and must be done on a periodical basis.