Hour of birth and birth assistance: from a primate to a medicalized pattern?

Previous studies generally agree that in Homo sapiens births without medical intervention occur mostly at night, although with a less accentuated pattern than in other primate species. The present study has three main objectives: (a) to establish the hourly pattern of births in a modern medicalized population, (b) to explore the association between the hour of birth and maternal and fetal variables and mode of delivery, and (c) to evaluate the risk for medical intervention at different hours of the day.

The hourly distribution of 25,779 deliveries at the "La Paz" Madrid University Maternity Hospital (Spain) has been analyzed. Two different multivariate analyses have been used to evaluate, respectively, the relationships between maternal and fetal characteristics and the type of birth and hour of delivery.

The increasing of unnecessary hospital interventions seems to have transformed the nocturnal pattern of birth into a diurnal one and may be contributing to the rise of preterm and low birth weight deliveries, reducing their probability of being breastfeed, and eliminating or transforming emotional and social support. Immigrant women present a higher frequency of the nocturnal pattern of delivery than their Spanish counterparts.

The predominant nocturnal pattern of birth seems to have disappeared in a Spanish highly medicalized population. However, the hallmark of primate nocturnal deliveries is evident when multiple births, malpresentation, Caesarean sections, and vaginal interventions are excluded. Possible consequences of diurnal birth include reduced infant-mother bonding, breast feeding, and later life reductions to health.