There were 672,261 live births in Flanders between 1999 and
2009. From these, 23,551 (3.5%) non-singleton births and a further
139 (0.02%) births with a gestational age below 24 or above 44 weeks were excluded. After excluding 122,936 (19.0%) deliveries
with missing information on one of the covariates, the final study