Wednesday, March 07, 2007

C-section rates and the calculation of risk

The March 1 issue of the New England Journal of Medicine has a commentary on the current C-section rate. In Cesarean Delivery and the Risk–Benefit Calculus, Ecker and Frigolleto begin by describing the current situation:
In 1937, an article in the Journal describing 10 years of births at Boston City Hospital revealed an overall rate of cesarean delivery of about 3%. Recently released 2005 data on cesarean deliveries show that contemporary rates are 10 times as high,.. Indeed, of the 20th century's many changes in obstetrical care ... few have generated more attention and debate ... than this seemingly inexorable rise.
The rising rate of cesarean section has been closely associated with the increasing safety of the procedure.
In 1937, 6% of primiparous patients died after cesarean delivery, a risk that has decreased by a factor of nearly 1000 ... Certainly, in earlier eras, the specter of death during childbirth hovered over each decision to proceed to cesarean delivery, and everyone involved tolerated a greater degree of risk of maternal or neonatal complications from vaginal delivery than we accept today. As the risk associated with cesarean delivery decreased, practitioners and patients felt more comfortable choosing this option, even in situations in which there was less potential benefit ...
Critics claim that the rising C-section rate is the result of doctors attempting to maximize profit and convenience, but the authors note that the C-section rate is rising around the world, and in countries where the economic incentives are very different. They believe that the increase is due, in large part, to the profound changes in both patient and provider calculations of risk and in the changing expectations of how much risk is appropriate.
Vaginal breech deliveries are no longer recommended, since the 3% associated neonatal morbidity has been judged excessive, and such deliveries have been abandoned. Careful and repeated study of a trial of labor after prior cesarean delivery has led some to conclude that elective repeated cesarean delivery, because it is associated with lower rates of major complications (including uterine rupture) and lower rates of poor perinatal outcome (including hypoxic–ischemic encephalopathy), is "safest," ... Furthermore, better data describing the complications associated with the use of forceps or vacuum extraction ... have led to a decrease in the number of operative vaginal deliveries (from 9.5% in 1994 to 5.6% in 2003) that parallels the increase in cesarean deliveries ...
Critics of the current C-section rate claim that many cesarean sections are unnecessary, in retrospect. Obstetricians know this, but they also know that many C-sections must be done to prevent rare, but serious complications:
For example, among women without gestational diabetes whose fetuses have an ultrasound-predicted weight of more than 4500 g (10 lb), it has been estimated that 3695 cesarean deliveries are needed to prevent one permanent brachial plexus injury — a number that reflects both the imprecision of in utero estimations of fetal weight and the reality that most large infants will undergo vaginal delivery without injury. To cite another example, "only" 3% of infants with breech presentation who are delivered vaginally will have traumatic injury. And most babies delivered by cesarean section because of a "nonreassuring" fetal heart-rate tracing are born healthy and vigorous, reinforcing the perception that cesarean deliveries are not needed in such circumstances.
As Ecker and Frigoletto point out, the most important variable is the level of risk that is considered acceptable:
But the key question centers on both the number needed to treat to avoid one adverse neonatal outcome and the level of risk that is currently considered acceptable... [T]he risk that women are now willing to assume in exchange for a measure of potential benefit, especially for the neonate, has changed: for many, the level of risk of an adverse outcome that was tolerated in the past to avoid cesarean delivery is no longer acceptable, and the threshold number needed to treat has thus been reset.


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