Circadian variation in the circumstances of delivery in a population at low obstetric risk

While circadian variations in birth and perinatal mortalityrates have previously been described in the literature, thereasons behind these observed rhythms remain unclear. The principalhypothetical causes include variations in obstetric practicesand an association between the time of birth and biologicalparameters. In order to explore this issue we analysed the distributionpatterns for time and day of birth, as well as circadian variationsin maternal characteristics, obstetric practices and neonatalrisk in a population at low obstetric risk. The study populationincluded 685 low-risk pregnant women consecutively admittedat an early stage of labour to six maternity units. The resultsshowed hourly variations in the birth rate and circadian variationsin obstetric practices that might explain the hourly patternobserved for the birth rate. By contrast, the frequency of apositive neonatal risk indicator was uniform across all timecategories in this population at low obstetric risk.