Available data suggest a role for the fetal hypothalamic–pituitary–adrenal system in the initiation of spontaneous labor as well as a physiologic response to melatonin secretion in the regulation of natural labor onset.1,9–13 Older studies suggested that natural labor onset peaked around midnight and that nocturnal labor is significantly shorter than diurnal labor.1,14 This predominantly nocturnal pattern of birth in humans and other primates has been seen as an advantageous evolutionary adaptation to reduced predation and the availability of group social support at night.1 However, more recent data suggest that the historic nocturnal pattern of birth has largely been reversed with most deliveries occurring during the day; unfortunately, such data are often confounded by the temporal effects of medical intervention.1,2
In a similar manner, recent data document a shift in the peak of the distribution curve of human birth from 40 to 39 weeks of gestation, a change generally attributed to an increased tendency for artificial intervention in the birthing process.4,5
To further investigate these possibilities, we examined a hypothetical model in which an initially normally distributed population of similar size with a peak at 40 weeks of gestation is depleted by random elimination of data points beyond 39 weeks of gestation.
The preoffice hours spike in cesarean deliveries is, to a significant degree, related to scheduled repeat cesarean deliveries and as such is not of particular concern from a quality standpoint. However, the lunch time and immediate postoffice hours spikes in overall cesarean deliveries and the spikes seen at all three times for primary cesarean deliveries are of concern because labor arrest disorders are the most common indication for primary cesarean delivery and recent data suggest that a primary driver of such indications is failure to allow sufficient time before making the diagnosis of first- and second-stage labor arrest.22–24 The conclusion that decisions regarding primary cesarean delivery may be influenced by nonmedical factors is confirmed in Figure 8, which demonstrates a statistically significant increase in the likelihood of primary cesarean delivery on weekdays as compared with weekends. Only 1.5% of primary cesarean deliveries in our system are elective (patient choice).25 If one assumes that the rate of weekend primary cesarean deliveries more accurately reflects decisions based on medical necessity without the influence of weekday practice considerations, Figure 7 suggests that approximately one third of primary cesarean deliveries in nulliparous women might be avoided without compromising patient safety simply by altering the current system of intrapartum care to make everyday a weekend day in terms of physician convenience.
The well-documented representative nature of both demographics and practice within our hospital system and a system-wide cesarean delivery rate at the national average suggest that these observations are not unique to our system but apply generally to obstetric practice in the United States.6–8,22,25 Indeed, recent data from our system demonstrate that cesarean delivery rates may be reduced with a hospitalist model of obstetric care in which delivery decisions are unencumbered by personal, sleep, or office practice considerations.26,27 In contrast, the current approach to care in the United States generally reflects a system in which the need to perform a delivery almost always represents a distraction from some other personal or professional activity. In this respect, the observation that every system is perfectly designed to achieve exactly the results it is achieving would seem to apply.28 Attempts to reduce the cesarean delivery rate by changing engrained modes of individual physician practice are important. These include proper interpretation of fetal heart rate tracings and appropriate management of labor arrest. However, without the type of systems changes recommended by the Institute of Medicine, such changes are by themselves likely to prove as ineffective in the future as they have in the past.29,30
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