Why does the prevalence of low birthweight increase in Berlin?

Introduction: Infant and newborn mortality decreased in Germany during the last decade, while the prevalence of low birth weight increased. The objective was to evaluate which risk factors for low birth weight might be responsible for this increase. Material and Methods: Data of the Berlin Perinatal Statistics from 1993 through 1999 on 181700 newborns were analysed by univariate and multiple logistic regression equations. Results: From 1993 through 1999 the rate of birth weights below 2500 g in Berlin increased significantly from 6.9% to 7.5% per year (p<0.001). The prevalence of premature births increased significantly as well as that of multiplets, of firstborns, of the mother's age, but also of their initial weight, height and body mass index. The prevalence of smokers in pregnancy was constant over this time period, the mean gestational age of newborns decreased significantly. By logistic regression equation 62% of the variance of low birth weight could be explained by the risk factors multiple birth, smoking in pregnancy, age of the mother, female sex, primiparity, German nationality, year of birth and additionally by the protective factors pregnancy duration, initial weight of the mother, BMI, and weight gain in pregnancy. Conclusions: The increase in low birth weight over the last years can be explained by indicators of reproductive medicine.