[Daily number of births in Norway 1989-93. Variations across months, day of week, phase of the moon and changes in leave entitlements].

The variation in the daily numbers of births across month, day of week, phase of the moon and maternity leave entitlements have been studied for all births in Norway between 1989 and 1993, a total of 302,209 newborn children. The number of births was highest in the spring and lowest in November and December. A secondary birth maximum was observed in September, possibly related to activities during Christmas and New Year celebrations nine months before. Furthermore, births were least numerous at weekends and were concentrated in the middle of the week. This pattern probably reflects less active obstetric intervention at weekends. The number of births does not seem to vary with phase of the moon. At the time of the latest, and largest increase in national birth maternity leave entitlements, fewer births occurred in the days before and correspondingly more births in the days immediately after the date when the change came into force.