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.