Influence of elective preterm delivery on birthweight and head circumference standards

We calculated new birthweight and head circumference centiles for boys and girls between 24 and 42 weeks' gestation from 20,713 singleton live births at our hospital between 1978 and 1984. Among the 803 babies born at or before 34 weeks' gestation, 28% were delivered electively for fetal problems; they were considerably lighter than babies born after spontaneous preterm labour. In contrast, they showed only a small deficit in head circumference, possibly due to a brain sparing effect in growth retarded infants. Electively delivered preterm infants cause a bias in birthweight and head circumference centiles and we recommend that these babies should be excluded when these centiles are calculated.