Revisiting the daily human birth pattern: time of delivery at Casa de Maternidad in Madrid (1887-1892).
OBJECTIVE
Among the ancestral characteristics of the primate group to which Homo sapiens belongs we find a pattern of daytime physical activity, but one notable exception is birthing which usually begins with night-time labor. In populations with a moderate or high level of medicalized labor, there is evidence that the medical preferences interfere with the underlying biological mechanism for the circadian pattern of human birth.


METHODS
This study analyses the hourly patterns of 4,599 single live births in the House of Maternity in Madrid between 1887 and 1892, a period of very limited obstetric intervention and without the influence of artificial lighting. In order to determine the influence of natural light on labor, two periods of maximum and minimum light have been established around the summer and winter solstices of the years in question.


RESULTS
A clear circadian pattern of births emerges, with very early morning and early morning births dominating, and a sharp drop from midday until nightfall. The hourly distribution on both solstices follows this pattern, but with a clear peak shift: in winter, there is a greater concentration of deliveries in the early morning, whereas in the summer, the highest concentration is between 8 and 12 in the morning.


CONCLUSIONS
The results confirm that non-intervened human birth has a clear diurnal cycle, with a higher incidence of deliveries in the early morning or morning. The shift in distribution during the winter and summer solstices seems to confirm the effect of light on the labor process.
Department of Biology, Madrid Autonomous University, Madrid, 28049, Spain.
Carlos
C
Varea
Susana
S
Fernández-Cerezo
D002940:Circadian Rhythm; D036861:Delivery, Obstetric / Q000266:history*; D005260:Female; D049672:History, 19th Century; D006801:Humans; D036801:Parturition; D012621:Seasons; D013030:Spain