title: Seasonality of mean birth weight and mean gestational period in Japan.
abstract: Seasonal variations of mean birth weight from January 1974 to December 1983 and of mean gestational period from January 1979 to December 1983 in Japan are analyzed by time-series analysis. This analysis decomposes the variation in a series into trend, seasonal variation, other cyclic changes, and a remaining irregular fluctuation. The results of the present analysis support the existence of a seasonal rhythm of mean birth weight and mean gestational period in Japan with statistical significance (p < 0.001). Seasonal patterns of mean birth weight show two peaks in May and October-November and two troughs in June-September and December. Mean gestational periods shows two peaks in October and February-March and a deep trough in winter and a much smaller one in June-September. Two time series demonstrated a coincidence in monthly variations with statistical significance. These results indicate that a part of seasonality in birth weight could be explained by the seasonal variations in mean gestational period.
authors.affiliation: Department of Human Ecology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Matsuda
authors.forename: T
authors.initials: T
authors.lastname: Sone
authors.forename: T
authors.initials: T
authors.lastname: Doi
authors.forename: H
authors.initials: H
authors.lastname: Kahyo
mesh_terms: D000367:Age Factors; D000704:Analysis of Variance; D001724:Birth Weight; D005260:Female; D005313:Fetal Death / Q000453:epidemiology; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007564:Japan / Q000453:epidemiology; D016018:Least-Squares Analysis; D008297:Male; D010298:Parity; D012621:Seasons