['To investigate the relation between use of epidural analgesia (EDA) and maternal and fetal characteristics.', 'Population-based register study.', 'Nationwide study in Sweden.', 'All 106,775 primiparous women who in 2002-2005 delivered a singleton infant vaginally at term.', 'Register study with data from the Medical Birth Registry and the Swedish Register of Education.', 'Use of EDA during vaginal delivery.', 'A total of 47,810 women (45%) received EDA during labor. EDA was used more often in women who were either young or short, had a high body mass index or a short education, or gave birth to an infant with high birthweight. After adjustment, the positive correlation with birthweight persisted. The use of EDA was twice as high in women with infant birthweight >4,500 g, 60% higher in those with infants weighing between 4,000 and 4,500 g and 25% lower when infants weighed <3,000 g, when compared to those with newborns weighing between 3,000 and 3,500 g.'] Is the need for epidural analgesia related to birthweight - a population-based register study?