An alternative approach to the creation of fetal growth standards

Fetal weight, determinined by ultrasonography, and weight at birth are used to assess growth status which is important for clinical decision making. Fetuses or infants whose birth weight is less than the 10th percentile or the 3rd percentile of a fetal growth standard are deemed to be small-for-gestational age. Those whose birth weights exceed the 90th or 97th percentile are deemed to be large-for-gestational age. Small-for-gestational age babies and also babies who are large-for-gestational age experience perinatal mortality and serious neonatal morbidity at rates that are considerably higher than those observed among babies that are appropriate-for-gestational age. Fetal growth standards are created by examining the birth weight of a large series of live births at each gestational age and identifying percentiles of birth weight at each gestational age. This approach involves numerous questionable assumptions even though it has enormous face validity. Our preliminary work shows that current fetal growth standard yield contradictory findings in terms of mortality patterns. We propose to develop fetal growth standards using an alternative approach. This will involve identifying the birth weight (at each gestational age) at which rates of mortality and morbidity are the lowest and then obtaining cut-off for small-for-gestational age and large-for gestational age based on patterns of mortality and morbidity and non-optimal birth weights. For this study we plan to use the Canadian Vital Statistics and hospitalization databases, the National centre for Health Statistics database of the United States and the Novs Scotia Atlee Perinatal database. Study investigators are familiar with these databases and have published related and unrelated studies using these databases.