Survival of the smallest. Time trends and determinants of mortality in a very preterm population during the 1980s.

In a regionally representative preterm birth cohort, the fetal to first year survival of very preterm infants born at 32 weeks' gestation or less increased from 54% to 66% between 1978 and 1986. This improvement was due to a fall in numbers of stillbirths while neonatal mortality either declined or remained the same. Only among extremely immature preterm babies born at 26 weeks or less was improvement in fetal survival counteracted by an increase in neonatal mortality. Fewer than 5% of complete fetal to first year deaths occurred postneonatally. After the age of 26 gestational weeks, intrauterine growth retardation was a major unfavourable factor, associated with a 3-fold increase in neonatal mortality.