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Indeed, 21st-century pregnant women and their pregnancies differ from those of previous eras. Parturients are now heavier than they used to be (one 21-year study found a doubling of obesity rates), and they are older (there has been a 3.8-year increase since 1970 in the mean age at first delivery, and since 1990, births to women 35 to 39 years of age and 40 to 44 years of age have increased by 43% and 62%, respectively). In addition, the number of premature and low-birth-weight neonates has increased, in part as a function of the increasing number of multiple gestations (121,246 in 2001 vs. 68,339 in 1980), many of which have resulted, in turn, from the use of assisted reproductive technology — assistance necessitated in many cases by advancing maternal age. All these changes have been associated with an increased risk of cesarean delivery.
Evidence-based recommendations founded on outcomes data are increasingly influencing obstetrical care and changing practice. 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,"3 and among women who have had a cesarean delivery, fewer now choose a trial of labor in their next pregnancy (see graph). Furthermore, better data describing the complications associated with the use of forceps or vacuum extraction — neonatal birth injury and maternal perineal trauma and incontinence — 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; as obstetricians perform fewer operative vaginal deliveries, they grow less comfortable with the methods, and the decrease becomes self-perpetuating. Finally, in 2003, 20.6% of labors were induced, as compared with 9.5% in 1990. Some inductions result from increased use of antenatal fetal surveillance and the real or perceived fetal jeopardy that is detected. Inductions may also be scheduled for convenience — for example, to allow parents to organize work and child-care schedules or to allow providers to be on call when their patients deliver. Most studies link inductions to increased use of cesarean delivery.
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Balanced against all these influences pushing the cesarean rates higher are the method's associated risks and consequences. Apart from the immediate operative risks — including infection, the need for blood transfusion, damage to pelvic organs, and postoperative pain — specific objections to cesarean delivery include concern regarding a mother's future reproductive health, since later pregnancies are associated with increased risks of miscarriage, ectopic gestation, placenta previa, and placenta accreta. These risks are real and have been well described, yet when making decisions, patients and their providers often think only within the context of the current pregnancy, especially since future reproductive plans may be uncertain.
More generally, to critics of the rising cesarean rate, many cesarean deliveries seem unnecessary — unlikely, in their evaluation, to meaningfully improve neonatal or maternal outcome. And many cesarean deliveries do appear at first glance to be unnecessary. 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.5 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.
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. As practicing obstetricians, we find that the 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.
In the face of the resulting continued increase in cesarean deliveries, our obligation as providers is to educate patients about the trade-offs entailed in choosing a particular course or intervention and to ensure that their choices are congruent with their own philosophy, plans, and tolerance of risk. In areas in which there is still uncertainty, we must organize clinical trials that will produce the data we require for counseling patients. For the moment, however, few of the relevant factors seem likely to change, and the cesarean rate can be predicted to continue its climb.
Source Information
Dr. Ecker is an associate professor and Dr. Frigoletto a professor of obstetrics, gynecology, and reproductive biology at Harvard Medical School, and both are obstetricians at Massachusetts General Hospital, Boston.
An interview with Dr. Ecker can be heard and a slide presentation can be seen at www.nejm.org.
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