Birthweight centiles in preterm infants. A new approach

To analyze the birth weight of preterm infants developing a new methodology in order to efficiently collect data.

We have analyzed the birthweight of 2,482 preterm babies with a gestational age between 24 and 36 weeks admitted to a Neonatal Intensive Care Unit from 1991 to 1998. The gestational age was determined from obstetric data. No selections were performed at the earlier stages of the study by excluding newborns with congenital defects, sepsis, intrauterine growth retardation or obstetric pathologies. More selective criteria were applied at the final stage by using statistical tests. The anomalous and extreme weights for every gestational age were identified with Box and Whisker graphs. The clinical records of these cases were analyzed and their characteristics described but these weights were excluded from the calculation of the percentiles. For each gestational age we evaluated if the weight distribution was assimilable to normal distribution by calculating the kurtosis, asymmetry by applying the Kolmogorov-Smirnov and Shapiro test.

In the majority of cases we found a normal weight distribution.

The proposed methodology seems useful in making data collection for preterm centiles calculation simpler. A study of the clinical characteristics of the SGA and LGA identified with the normal procedure or with the proposed method might be useful in validating our approach to the definition of the percentiles.