FURTHER MAPPING OF THE NATALITY CHRONOME IN TODA CITY (JAPAN) MATERNITY HOSPITAL

In order to investigate any circannual and/or circaseptan variations in birth incidence and birth weight in Toda City (Japan), data on 4,411 consecutive births were obtained from the city's Maternity Hospital between 1 Jan 1999 and 31 Dec 2001. Data were analysed by cosinor separately for babies with birth weights in given ranges, and separately for boys and girls born at different gestational ages. A circannual rhythm was detected with statistical significance (P=0.047) for birth incidence of all vaginal deliveries, with an acrophase in the fall. A similar result for caesarean sections was of borderline statistical significance. A circaseptan component with a relatively consistent acrophase around midweek was of borderline statistical significance for birth incidence in some of the groups investigated. About-yearly and about-weekly variations were also found to characterize birth weight in some of the groups investigated.