Covariates
The interpregnancy interval (IPI) is defined as the interval between
prior birth and conception date of the subsequent pregnancy using the
expected due date and gestational age. The IPI was subdivided into 0-3,
3-6, 6-12, 12-36 and >36 months. Gestational age was based
on crown-rump-length (CRL) during early fetal sonography. Assisted
reproductive technology (ART) yes/no. Birth weight is shown in grams.
Low social economic status (SES) of a neighborhood was defined based on
income, paid jobs and education. Low SES (most deprived) was defined as
SES at the lowest quintile.