Strengths and Limitations
An important strength of our study was the linkage of our prenatal
ultrasound cohort to population-based follow-up data. This enabled us to
obtain longer-term child health outcome information without differential
losses to follow-up, a common concern with prospectively-collected
follow-up methods. This also enabled us to compare characteristics and
outcomes in this higher-risk cohort (i.e., with an indication for third
trimester prenatal ultrasound) to that of the general population. Our
use of the Early Development Instrument, a validated indicator of
kindergarten readiness and developmental vulnerability used in multiple
jurisdictions worldwide, is also a strength as it enables our findings
to be contextualized within a large body of literature on other risk
factors for adverse child development.
Limitations of our study include the lack of EDI test results for a
large fraction of the cohort. However, as these data are missing due to
administrative reasons (the 3-year duration of testing waves across the
province), this is unlikely to have introduced bias to our study. It did
reduce our sample size, but our cohort of over 3400 children is still
one of the largest studies of school-aged outcomes following prenatal
ultrasound available. Our studied examined small fetal size (small for
gestational age [SGA]), which is recognized to be a flawed indicator
of the true pathological process of interest, fetal growth restriction.
However, as fetal weight percentiles are widely used to screen for
high-risk fetuses clinically, our evaluation of the predictive ability
of SGA status provides pragmatic information on a commonly-used tool for
clinical care.