An increasing proportion of infants weigh more than 4000 grams at birth

Background. To investigate how mean birthweight has changed in the past dec ade, and to describe changes in the proportion of infants with a birthweigh t above 4000 grams (g). Methods. We analyzed data on 43,561 singleton infants born between 1990 and 1999 at Aarhus University Hospital, Denmark. Information on birthweight, g estational age, stillbirths, malformations, mode of delivery, prelabor inte rvention, and maternal diabetes was obtained from birth registration forms. Results. For all infants mean birthweight increased by 45 g (95% CI: 20-70 g) from 3474 g: in 1990 to 3519 g in 1999. For infants born at term the mea n increase was 62 g (95% CI: 41-83 g). During the same period the percentag e of infants born with a birthweight. above 4000 g increased from 16.7% in 1990 to 20.0% in 1999 (p<0.05). Simultaneously we found a decrease in gesta tional age and an increase in the frequency of induction of labor. There wa s a statistically significantly higher risk of giving birth to an infant wi th a birthweight above 4000 g throughout the decade, when gestational age a nd prelabor intervention was taken into account. Conclusions. In Denmark mean birthweight has risen during the past decade i ndependently of gestational age and prelabor intervention. Simultaneously t he risk of having a baby with a birthweight above 4000 g has increased. Fur ther studies on potential risk factors for birth of large infants are neede d.