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.