Cesarean Sections in the U.S.: The Trouble with Assembling Evidence from Data

U.S. Cesarean Section Rates

Surgery detail

Pregnancy, labor, and delivery have become increasingly medicalized in recent decades, leading to criticism from multiple factions. For instance, the rate of cesarean section in the U.S. (and in many other developed nations) draws fire from the World Health Organization (WHO), which suggests that the c-section rate should not rise above 15% [1].

There?s no doubt that the rate of c-section is high in the United States compared to elsewhere in the world. In 2009, cesareans accounted for 32.9% of all deliveries, up from 20.7% in 1996 [2]. Worldwide, rates of c-section vary tremendously, with cesarean rate being very nearly a proxy measurement for access to skilled birthing assistance. According to WHO, the least developed countries have c-section rates averaging around 2%, while the most developed regions average just above 20% [3]. In fairness, these numbers can?t be compared directly to the current c-section rate in the U.S., as they are several years old. At the time of the WHO report, the U.S. c-section rate was around 27.6%.

Induction of labor is a relatively common birthing intervention in the U.S., occurring in 23% of all pregnancies [2]. There is a well-established relationship between induction of labor and increased risk of c-section [4, 5], with one study estimating that induction itself contributed to eventual cesarean in approximately 20% of induced labors (other contributing factors aside) [6]. Another study suggested that induction more than doubled the likelihood of a c-section [7].

Is The Cesarean Rate A Problem?

While it?s tempting to look at the data and make the assumption that over-medicalization is responsible for the high rate of induction and c-section in the U.S. ? and to further extrapolate that the high rate of c-section is responsible for increased maternal mortality ? there are several problems with this interpretation. First, it goes without saying that c-sections, while not medically necessary in the majority of deliveries, are lifesaving for both mother and infant when medically required. Per WHO data, those undeveloped nations with the very lowest c-section rates have staggeringly high maternal mortality, with more than 1 in 100 labors resulting in the mother?s death. By comparison, maternal mortality in much of Europe and North America is in the range of 0.001 ? 0.03% [3]. This somewhat deromanticizes the image of a native tribeswoman squatting in her hut, giving birth ?as nature intended.? It?s easy to forget that if we desire completely natural childbirth, we have to accept the natural maternal and neonatal mortality that accompanies it.

Further, despite the link between induction and increased risk of c-section, judiciously used induction can actually prevent surgical intervention. A study of women at 41 weeks? gestation found that those who underwent induction were 12% less likely to require a c-section than those allowed to go into labor naturally [8]. There?s also significant evidence that pregnancies that go past 42 weeks are associated with increased neonatal morbidity (harm) and mortality [9]. Given the relatively low percentage of American women ? 5.5% ? who give birth at or after the 42-week mark, however, appropriate use of induction in the case of a post-term fetus can?t explain the c-section rate in the U.S.

Judicious and appropriate use of the c-section aside, there?s considerable evidence that non-medically indicated c-sections pose a risk to the mother. A study that excluded women with complications of pregnancy found that c-section was associated with a threefold higher maternal mortality as compared to vaginal delivery [10]. Planned c-sections are quite a bit safer than unplanned c-sections, according to the data. One study showed no difference in maternal mortality or serious maternal morbidity between planned c-section and vaginal delivery [11], while another showed a reduced risk of certain negative maternal outcomes ? including hemorrhage ? with planned c-section [12]. A third showed a modest increase in risk to the mother with regard to normal complications of surgery (including wound bleeding, longer hospital stay, and reactions to anesthetic). There was no increase in maternal mortality as compared to vaginal delivery, however [13]. With regard to the infant, mortality and serious morbidity are significantly lower in the case of a planned c-section than in that of a planned vaginal delivery [11]. Neonatal morbidity and mortality risk in cases of unplanned c-section are difficult to quantify accurately, since complications resulting in the need for a c-section are significant confounding factors.

With regard to long-term effects of cesarean delivery on the infant, there?s been some interest in a so-called ?hygiene hypothesis,? which suggests that vaginal delivery helps to colonize the infant gut with healthy bacteria [14]. As yet, however, this hypothesis is unproven. Studies have found no difference in long-term risk of death or developmental consequences associated with c-section delivery [15], and evidence supports the ability of the mother and infant to bond appropriately regardless of delivery type [16]. There is evidence that neonatal morbidity and mortality in a subsequent pregnancy are higher if the mother delivered by c-section in her first pregnancy [17]. However, this data is difficult to interpret in a meaningful way, since many c-sections are the result of complications of pregnancy, increasing the likelihood of a subsequent complicated pregnancy.

Based upon the data, it?s reasonable to conclude that an uncomplicated vaginal delivery is safest for mother and baby, while a planned c-section is safer than a complicated vaginal delivery that results in an unplanned c-section. Unfortunately, it?s impossible to know in advance who will have an uncomplicated vaginal delivery.

Possible Influences On Cesarean Section Rates

One theory regarding the high rate of c-sections in the U.S. as compared to those in certain other developed nations holds that the litigious nature of American society creates fear, and therefore overreaction, in the obstetrician. There?s some support for this theory; the likelihood of a c-section is indeed higher in cases in which there is greater risk of a malpractice suit [18]. Further, a survey of obstetricians revealed that physicians were more likely to comply with a request for cesarean delivery (in a medically ambiguous case) if they perceived a greater threat of litigation [19].

However, while the threat of suit may partially explain the c-section rate in the U.S. (in an unquantifiable way about which we may only speculate), it?s reasonable to assume that most obstetricians are interested first and foremost in good patient outcomes. After all, obstetrics is one of the medical specialties with the highest rates of lawsuit. If a physician?s sole motivation were to minimize the risk of litigation, that physician would be better off in another specialty.

There are other factors unique to the U.S., however, that could help explain the c-section rate. First, while obesity is a problem in much of the world, nowhere is it as epidemic as in the U.S. Currently, 36% of U.S. men and women are obese [20], while another third of Americans fall into the less severe ?overweight? category [21]. No other nation comes close to competing; obesity rates are around 26% for both men and women in the U.K., and around 25% for both genders in Australia and New Zealand. In Italy and Germany, approximately 20% of the population is obese, with lower rates still in France. Sweden has 11% obesity among women, with a rate of 15% among men [20]. Excess body fat is associated with a significantly increased risk of complications of pregnancy, including gestational diabetes and high blood pressure [22]. Even among women who are not significantly overweight or obese pre-pregnancy, the rate of excess pregnancy-related weight gain is high, with 20.8% of pregnant American women gaining more than 40 pounds [2]. For comparison purposes, most women are advised to gain 25-35 pounds during pregnancy. Excess weight gain during pregnancy is, like pre-pregnancy overweight and obesity, associated with increased risk of gestational diabetes and other complications. The rate of gestational diabetes in the U.S. is currently 4.8%, while the rate of pregnancy-related high blood pressure is around 4%, an increase of 50% over 1990 levels [2]. Both obesity and diabetes significantly increase the risk of cesarean delivery [23, 24]. Excess body fat decreases the rate of cervical dilation and protracts labor, both of which increase the likelihood of cesarean. Overweight women are about 1.2 times more likely than normal weight women to require a c-section [25, 26], while obese women are around 1.7 times more likely than normal weight women to require a cesarean [26, 27]. Adjusted for American overweight and obesity rates, the 32.9% c-section rate becomes 26.15%, which is closer to the rates observed in leaner developed nations.

Obesity is not the only factor that fundamentally affects the c-section rate. One of the benefits of modern obstetric technology is that women can maintain higher-risk pregnancies than ever before. Further, women who are infertile or past their peak of fertility can receive reproductive assistance and become pregnant. Delivery by cesarean is strongly and positively associated with advanced maternal age; while the c-section rate in 2009 was 32.9% for all women, it was lowest in the youngest mothers (22.3% and 27.4% for women younger than 20 and 20-24 respectively), and highest in the oldest mothers (40.6% and 46.7% for women 35-39 and older than 40 respectively) [2]. From an evolutionary perspective, it?s intuitive that the women best able to deliver their babies vaginally would be the younger ones. For the majority of human history, the average life expectancy has been about 30 years [28], indicating that women did not evolve to engage in routine vaginal delivery into their 30s and 40s. That c-section rate is a proxy measure for availability of medical care isn?t necessarily an indication that practitioners, by definition, overuse c-section. The association must be at least partially attributed to the fact that the most developed nations ? those with greatest access to medical care and some of the highest c-section rates ? are those very nations in which women can utilize medical technology to conceive where they would otherwise be incapable of doing so.

Furthermore, women of advanced maternal age and those who receive fertility treatments of certain types have increased probability of giving birth to twins or higher order multiples. In fact, the rate of twins born in the U.S. has increased dramatically in recent years, nearly doubling since the 1980s. Increases have been highest among older mothers. In 2009 alone, the twin birthrate increased by 2% over that of 2008, while the rate of higher-order multiples rose by 4% in a single year [2]. These increases are typical of recent years. Interestingly enough, the c-section rate has also been climbing by about 2% a year. While this is an intriguing correlation, it?s not a basis for suggesting that the increased prevalence of multiples is solely responsible for the rising c-section rate. Still, as most twins and higher-order multiples are delivered by cesarean, there is certainly a connection.

Then, too, there?s the simple fact that the modern c-section has been performed for almost 150 years, which is enough time to observe changes in the prevalence of certain genes on a population level. Women with small or unusually shaped pelvic openings who produced babies too large to fit through the pelvis (fetal-pelvic disproportion) were once at a great reproductive disadvantage. Before the modern c-section, such a woman would have been unlikely to produce a living child (or unlikely to survive her first delivery, which would have limited her to a single child). This would have decreased the prevalence in the population of genes associated with the many factors that can lead to fetal-pelvic disproportion. Now, however, such women are no longer at a reproductive disadvantage in those populations in which the c-section is commonly practiced. As such, the associated genes could reasonably be expected to become more prevalent in those populations, thus necessitating increasing numbers of c-sections. This is yet another intriguing (albeit unproven) forcing that could affect c-section rate.

Making Sense Of The Information

The question at the heart of all this is Do obstetricians in the U.S. do too many unnecessary c-sections? Unfortunately, this question is very problematic to answer. The major impediment to drawing strong, scientific conclusions about this issue is that the majority of birthing studies are non-randomized. This leads to significant confounding of the data, and makes generalizations difficult. For instance, an obese woman (higher risk of c-section) is more likely to be inactive than a non-obese women (higher risk of c-section [29]), and is more likely to have high blood pressure and/or diabetes than a non-obese women (higher risk of c-section). She?s also at higher risk of carrying a fetus with congenital abnormalities (30), which could negatively impact fetal health and increase the risk of a c-section. An obstetrician, knowing that this woman is at higher risk of a c-section, could very naturally approach the situation expecting to end up doing a c-section (and worrying about his liability because of this high-risk patient), both of which increase the patient?s risk of having a c-section. If, in the end, the woman has a c-section, is it because she needed it, or because she had so many risk factors that it didn?t make sense to wait? After all, the odds of a good outcome in a planned c-section are better than the odds of a good outcome in an emergency c-section, and the former is only slightly riskier to the mother ? and is less risky to the baby ? than a planned, uncomplicated vaginal delivery. Further, calculating the risks (to either mother or baby) associated with an emergency c-section is a difficult thing; after all, a c-section wouldn?t have been done on an emergent basis if there weren?t some indication of either maternal or fetal distress. It is therefore problematic to separate morbidity and mortality associated with the root cause of the distress from morbidity and mortality attributable to the surgery.

Ultimately, the c-section rate in the U.S. is likely affected by a number of factors, but may also owe much to risk-to-benefit analysis conducted by well-intentioned obstetricians, who are interested in maximizing maternal and neonatal wellbeing. Given that there are situations in which uncomplicated vaginal delivery is less likely, and given that a planned c-section is much safer than an emergency c-section, an obstetrician with any inkling that a patient could end up needing surgical intervention might reasonably conclude that scheduled surgery is the least risky of the available routes. It?s very easy ? assuming the baby was delivered successfully and the mother is well ? to look back on a c-section and call it unnecessary. This assertion, however, can?t be proven; it?s possible that both mother and baby would have come through a vaginal delivery in good health, but it?s also possible that the c-section was lifesaving. After the fact, there?s no way to know. In the end, the only cesarean that we can be absolutely certain was necessary is the one that, tragically, wasn?t done in time.

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