An analysis of birth weight by gestational age in Canada.

Birth-weight-gestational-age standards help to identify infants in need of special care and to determine causes and means for preventing retardation of intrauterine growth. Previously published standards either were based on small samples, data several decades old or characteristics of subpopulations in the United States or they were not specific for type of birth and sex. We compared the data for live births in 1972 with those in 1986 to develop current Canadian standards for type of birth (singleton or twin) and sex. We found that the 10th, 50th and 90th percentile figures for weight were slightly higher in 1986 than in 1972 for term deliveries (at 37 weeks' gestation or later), but the figures were virtually unchanged for preterm deliveries. The availability of reliable population-based standards should enhance the clinician's ability to identify true cases of retardation or acceleration of intrauterine growth.