Study population
We conducted a retrospective cohort study of non-anomalous, singleton
fetuses receiving an outpatient obstetrical ultrasound between 28 weeks,
0 days and 41 weeks, 6 days gestational age at the British Columbia (BC)
Women’s Hospital, Vancouver, British Columbia, Canada between April 1
2000 to March 31 2011. BC Women’s Hospital is a tertiary care teaching
hospital of the University of British Columbia. It is the primary fetal
and children’s referral centre for the province of British Columbia,
with an annual delivery volume of approximately 7000 births. Ultrasound
records were linked with British Columbia population-level health and
education databases, including the BC Perinatal Data Registry, which
contains abstracted obstetrical and neonatal medical records for
>99% of births in the province, and results from routine
province-wide kindergarten readiness testing. We restricted our analytic
cohort to fetuses with a valid estimate of fetal weight at or beyond 28
weeks’ gestation, with no major anomalies (based on the US Center for
Disease Control Definition of major anomalies). We obtained obstetrical
and neonatal health outcomes for all births in British Columbia to help
describe the source population from which our ultrasound cohort was
drawn.