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

BACKGROUND: To investigate how mean birthweight has changed in the past decade, and to describe changes in the proportion of infants with a birthweight 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, gestational age, stillbirths, malformations, mode of delivery, prelabor intervention, 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 mean increase was 62 g (95% CI: 41-83 g). During the same period the percentage 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 gestational age and an increase in the frequency of induction of labor. There was a statistically significantly higher risk of giving birth to an infant with a birthweight above 4000 g throughout the decade, when gestational age and prelabor intervention was taken into account.
CONCLUSIONS: In Denmark mean birthweight has risen during the past decade independently of gestational age and prelabor intervention. Simultaneously the risk of having a baby with a birthweight above 4000 g has increased. Further studies on potential risk factors for birth of large infants are needed.