Data were extracted from the Birthing Outcomes System, an electronic
database recording all births after at least 20weeks of pregnancy.
Data are entered into this database at the first hospital pregnancy care
(booking) visit and at birth, with routine data maintenance, cleaning,
and validation. Postcodes of residence were matched to corresponding
Index of Relative Socio-economic Disadvantage (IRSD) deciles [15], in
which the most socioeconomically disadvantaged geographic
areas are represented by 1, and the least disadvantaged areas by
10. Categories for maternal age, late booking visit (≥14 weeks of
pregnancy), low 5-minute Apgar score (b7), low birth weight
(b2500 g), preterm birth (b37 weeks of pregnancy), and post-term
birth (N41 weeks gestation) were consistent with Australia’s annual
perinatal reports [14]. Poor attendance was defined as two or
more booked pregnancy care